Mass sensor and mass sensing method

ABSTRACT

A mass sensor ( 30 ) in which a connection plate ( 33 ) and a diaphragm ( 31 ) are joined together at their respective sides; a sensing plate ( 32 ) is joined to the connection plate ( 33 ) at their respective sides in the direction perpendicular to the direction where the diaphragm ( 31 ) is joined to the connection plate ( 33 ); a piezoelectric element ( 35 ) consisting of a piezoelectric film and an electrode is installed on at least either one of plate surfaces of the sensing plate ( 32 ); and a resonating portion consisting of the diaphragm ( 31 ), the sensing plate ( 32 ), the connection plate ( 33 ), and the piezoelectric element ( 35 ) is joined to a sensor substrate ( 34 ). Change in the mass of the diaphragm ( 31 ) is measured by measuring change in the resonant frequency of the resonating portion accompanying the change in the mass of the diaphragm ( 31 ). The mass sensor of the present invention enables the easy and accurate measurement of a minute mass of a nanogram order including microorganisms such as bacteria and viruses, chemical substances, and the thickness of vapor-deposited films.

TECHNICAL FIELD

[0001] The present invention relates to a mass sensor for determining aminute mass of a nanogram (10⁻⁹ g) order, for example, a mass sensor forsensing microorganisms such as bacteria, viruses, and protozoa (immunesensor), and a mass sensor for sensing moisture, toxic substances, orspecific chemical substances such as taste components (moisture meter,gas sensor, and taste sensor), and, a method for sensing a mass. Inparticular, the present invention relates to a mass sensor, and a methodfor sensing a mass, conveniently used for determining the mass of a bodyto be sensed by measuring change in resonant frequencies caused bychange in the mass of diaphragm on which a catching substance forcatching a body to be sensed by reacting only with the body to be sensedis applied.

[0002] Since the mass sensor of the present invention is not limited tothe measurement of change in the mass of the catching substance appliedon a diaphragm as described above, that is, not limited to the indirectmeasurement of change in the mass of a diaphragm, but it is naturallypossible to sense change in resonant frequency due to change in the massof the diaphragm itself, the mass sensor can also be used as a thicknessmeter for vapor-deposited films or a dew point meter.

[0003] Furthermore, even if the mass of the diaphragm is not changeddirectly or indirectly, the mass sensor of the present invention canalso be used as a vacuum meter, a viscosity meter, or a temperaturesensor by placing it in an environment to cause change in resonantfrequency, that is, by placing it in an environment of medium gases orliquids having different degree of vacuum, viscosity, or temperature.

[0004] Thus, although the mass sensor of the present invention can beused in various applications depending on its embodiments, the samebasic principle is also applied to the measurement of change in resonantfrequencies of the diaphragm and the resonating portion including thediaphragm.

BACKGROUND ART

[0005] Recent progress of scientific and medical technologies, and newlydeveloped medicines such as antibiotics and chemicals have enabled thetreatment of various diseases heretofore considered to be difficult totreat. On the other hand, especially in developed countries where peopleare accustomed in such medical civilization, immunological resistance ofhuman beings have lowered, and many people have suffered from variousdiseases caused by substances or microorganisms which heretofore had nothurt human beings.

[0006] Among what are referred to as diseases, microorganismexaminations are essential for the treatment of diseases caused bymicroorganisms such as bacteria, viruses, or protozoa, to find theirpathogens, to clarify their types, and to determine drugs to which theyare sensitive.

[0007] At present, in the first stage of microorganism examinations,since the cause of a disease and the type of the pathogen can beestimated from the symptoms, various specimens, such as blood, areselected depending on the type of the disease, pathogens present in thespecimens are morphologically identified, or antigens or the specificmetabolites of pathogens (e.g., toxins or enzymes, etc.) existing in thespecimens are immunochemically identified. This process is smear,tinction, or microscopy used in bacterial examinations, and in recentyears, instantaneous identification has become possible ill this stageby fluorescent antibody tinction or enzymatic antibody tinction.

[0008] Furthermore, the virus serological test, recently used in thedetection of viruses, is a method for proving the presence of specificimmunity antibodies that appear in the serum of a patient. Examples ofthe method include the complement fixation reaction in which thepresence of antibodies or antigens is determined by adding complementsto test blood, and by observing whether the complements react withantigens or antibodies in the blood and fix to the cell membranes of theantigens or antibodies, or destroy the cell membranes.

[0009] Except extremely special cases where symptoms have not been seenheretofore, and the disease is caused by a new pathogen which has notbeen discovered, in the treatment of diseases caused by microorganismsor the like, adequate treatment can be conducted by finding pathogens inan early stage through the microorganism test described above, and thepatient can be led to recovery will out worsening of the symptoms.

[0010] However, with methods such as smear, tinction, and microscopy,the detection of microorganisms is often difficult depending on theirquantities, and time-consuming treatment such as the culture ofspecimens on an agar is required at need. Also in the virus serologicaltest, since measurements must be performed as a rule during both theacute stage and the convalescent stage for determination from themovement of the quantities of antibodies, there is the problem of timeconsuming from the point of view of prompt diagnosis.

[0011] As seen in complement fixation described above, when a substanceto be sensed reacts with a catching substance which catches thesubstance to be sensed by reacting only with specific substance to besensed, microorganisms, the mass of the catching substance increases bythe mass of the substance to be sensed, even slightly. Such an increasein the mass is similarly occurs in the relationship between a catchingsubstance and a chemical substance such as a specific gaseous substanceand a smell component, and also applies to the case where a substrateitself without change in the mass is a catching substance, on which aspecific substance is deposited or added. On the contrary, when areaction in which a substance to be sensed caught by a catchingsubstance or the like is released occurs, the mass of the catchingsubstance or the like slightly decreases.

[0012] As an example of a method for sensing change in such a smallmass, U.S. Pat. No. 4,789,804 discloses in FIG. 27 thereof a mass sensor80 comprising a quartz oscillator 81 and electrodes 82, 83 facing thequartz oscillator. When any substance adheres externally on theseelectrodes 82, 83, the mass sensor 80 senses change in their mass usingchange in the resonant frequency of the thickness slip oscillation ofthe quartz oscillator 81 in the direction of the surface of theelectrodes. Since such a mass sensor 80 measures change in resonantfrequency basically caused by change in the mass load on the quartzoscillator 81, such a mass sensor 80 is considered to be able to be usedalso as a thickness meter for measuring the thickness or the growth of avapor-deposited film, or a moisture meter.

[0013] However, when such a quartz oscillator 81 is used, since the parton which an external substance adheres and the part for detectingresonant frequency are in the same location, for example, the resonantfrequency is unstable when the piezoelectric properties of the masssensor 80 itself vary due to the temperature of the specimen or changein temperature. Also, if the specimen is a conductive solution, and whenthe mass sensor 80 is immersed unprotected in the specimen,short-circuit between electrodes may occur. Therefore, the mass sensor80 must be subjected to insulation such as resin coating.

DISCLOSURE OF INVENTION

[0014] The present invention aims to solve the above problems of amicro-mass sensor, and according to the present invention, there areprovided first to sixth mass sensors described below.

[0015] As a first mass sensor, there is provided a mass sensorcharacterized in that a piezoelectric element is arranged on at least apart of at least one plate surface of a sensing plate, a side of atleast one sheet-like diaphragm is joined to a side of said sensing plateso that the plate surface of said diaphragm is perpendicular to theplate surface of said sensing plate, the other side of said sensingplate is joined to a sensor substrate, and a resonance portion is formedof said sensing plate, said diaphragm, and said piezoelectric element.

[0016] Furthermore, as a second mass sensor, there is provided a masssensor characterized in that a connection plate is joined to a diaphragmat respective sides, a sensing plate is joined to said connection plateat respective sides in the direction perpendicular to the joiningdirection of said diaphragm and said connection plate, a piezoelectricelement is arranged on at least a part of at least one of the platesurfaces of said sensing plate, at least a part of sides of saidconnection plate and said sensing plate is joined to a side of thesensor substrate, and a resonance portion is formed of said diaphragm,said connection plate, said sensing plate, and said piezoelectricelement.

[0017] Furthermore, as a third mass sensor, there is provided a masssensor characterized in that a connection plate is joined to a diaphragmat respective sides, two sensing plates are joined to said connectionplate at respective sides in the direction perpendicular to the joiningdirection of said diaphragm and said connection plate so as to sandwichsaid connection plate, a piezoelectric element is arranged on at least apart of at least one of the plate surfaces of at least one of saidsensing plates, at least a part of sides of said connection plate andsaid sensing plates is joined to a side of the sensor substrate, and aresonance portion is formed of said diaphragm, said connection plate,said sensing plates, and said piezoelectric element.

[0018] Here, in the third mass sensor, it is preferable that saidpiezoelectric element is arranged on at least one of the plate surfacesof one of said respective sensing plates facing to each other via theconnection plates, and one or more, preferably a plurality of, slits areformed on the other sensing plate in the direction perpendicular to thejoining direction of said other sensing plate and said connection plate.It is also preferable that respective piezoelectric elements arearranged on the plate surfaces of said respective sensing plates facingto each other via the connection plates in at least the same direction,and that the polarizing direction of the piezoelectric film in saidpiezoelectric elements arranged on one of the sensing plates, and thepolarizing direction of the piezoelectric film in said piezoelectricelements arranged on the other sensing plate are opposite to each otherwith respect to the connection plates.

[0019] Next as a fourth mass sensor, there is provided a mass sensorcharacterized in that a connection plate and a sensing plate notdirectly joined to each other are joined to said diaphragm at respectivesides so that the joining directions with the diaphragm are parallel toeach other, said connection plate and said sensing plate are joined toone side of a sensor substrate, a piezoelectric element is arranged onat least a part of at least one of the plate surfaces of said sensingplate, and a resonance portion is formed of said diaphragm, saidconnection plate, said sensing plate, and said piezoelectric element.

[0020] As a fifth mass sensor, there is provided a mass sensorcharacterized in that an assembly of a diaphragm sandwiched with twoconnection plates by joining at respective sides is placed across theside surfaces of a depression formed on a sensor substrate, each of twosensing plates is placed across said connection plate and across thebottom side of said depression in the direction perpendicular to thedirection of said respective connection plates sandwiching saiddiaphragm, a piezoelectric element is arranged on at least a part of atleast one of the plate surfaces of said sensing plates, and a resonanceportion is formed of said diaphragm, said connection plate, said sensingplates, and said piezoelectric element.

[0021] Here, a depression means that formed from sides facing to eachother and the bottom side connecting such sides; however, in the presentinvention, the bottom side is not necessarily a plane, but shape of thebottom side may be changed variously unless the measurement of theoscillation and the resonant frequency of the diaphragm, such as theprovision of a depression or a projection in the bottom side isaffected.

[0022] As a sixth mass sensor, there is provided a mass sensorcharacterized in that an assembly of a diaphragm sandwiched with twoconnection plates by joining at respective sides is placed across athrough-hole formed on a sensor substrate, at least a plurality ofsensing plates are placed between said respective connection plates andthe side of said through-hole, or said diaphragm and the side of saidthrough-hole, in the direction perpendicular to the direction of saidrespective connection plates sandwiching said diaphragm, a piezoelectricelement is arranged on at least a part of at least one of the platesurfaces of at least one of said sensing plates, and a resonance portionis formed of said diaphragm, said connection plates, said sensingplates, and said piezoelectric element.

[0023] Here, in the sixth mass sensor, when the piezoelectric element isarranged on at least one of the plate surfaces in each pair of saidrespective sensing plates facing to each other via the connection platesor the diaphragm, it is preferable that one or more, preferably aplurality of, slits are formed on the other sensing plate in thedirection perpendicular to the joining direction of said other sensingplate and said respective connection plates. Also, when respectivepiezoelectric elements are arranged on the plate surface of each pair ofsaid respective sensing plates facing to each other via the connectionplates or the diaphragm in at least the same direction, it is preferablethat the polarizing direction of the piezoelectric film in saidpiezoelectric elements arranged on one of the sensing plates, and thepolarizing direction of the piezoelectric film in said piezoelectricelements arranged on the other sensing plate is opposite to each otherwith respect to the connection plates or the diaphragm.

[0024] In these second through sixth mass sensors, it is preferable thatthe diaphragm, the connection plate, and the sensing plate form a sameplane when joined to each other, that is, these members have almost thesame thickness. It is also preferable that the sensing plate is fittedin and joined to the depression formed by the connection plate and thesensor substrate. It is preferable for this that the diaphragm, theconnection plate, and the sensing plate are integrally formed from adiaphragm, and the sensor substrate is laminated integrally with thediaphragm and the base plate.

[0025] It is also preferable that a spring plate is bonded to one of oreach of plate surfaces of the connection plate, and this spring plate isjoined to the sensor substrate or the spring plate reinforcement. Atthis time, unlike the structure bonded using adhesives, it is preferablethat the spring plate is integrally formed with an intermediate plateintegrally inserted between the diaphragm and the base plate, orintegrally formed with the spring plate reinforcement integrally formedwith the diaphragm, and also integrally formed with the connectionplate. When a plurality of connection plates are used, it is preferablethat the assemblies of the connection plate and the spring plate havethe same shape. It is also preferable that the mass sensor has areinforcing plate joined to the side of said sensor substrate, and inthis case, it is preferable that the reinforcing plate is integrallyformed with the spring plate and the sensor substrate.

[0026] Since a catching substance reacting only with a substance to besensed and catching the substance to be sensed is applied on thediaphragm, the piezoelectric element measures change in the resonantfrequency of the resonating portion in the state when the substance tobe sensed has not been caught by the catching substance, and in thestate after the substance to be sensed has been caught by said catchingsubstance, all the mass sensors according to the present invention issuitably used in the applications to measure the mass of the substanceto be sensed caught by the catching substance.

[0027] It is preferable that at least two resonating portions are placedon the sensor substrate, and the catching substance is not applied toone of the diaphragm of the resonating portions to use this diaphragmfor referencing. On the other hand, it is also preferable that differentcatching substances are applied to each resonating portion, that is, aplurality of resonating portions to which more than one of differentcatching substances are separately applied are provided in a sensor.Here, more than one resonating portions may be placed on the sensorsubstrate so as to expand the dynamic range by integrating the signalsfrom the respective resonating portions. Also, a through-hole of anoptional shape may be formed inside said sensor substrate, and theresonating portion may be formed on the internal circumferential surfaceof the through-hole.

[0028] It is also preferable to improve sensitivity, that one of thepiezoelectric element is split into two portions; one is used fordriving and the other is used for sensing. Furthermore, it is preferableto improve sensitivity, that two piezoelectric elements are placed onone resonating portion, and one of the piezoelectric elements is usedfor driving and the other is used for sensing. Therefore, each of thetwo piezoelectric elements placed on a resonating portion may be furthersplit into two portions, and in this case, each of the two piezoelectricelements has both driving and sensing functions.

[0029] Furthermore, when the specimen is a conductive solution, it ispreferable to provide a position sensor consisting of a pair ofelectrodes on the middle between the diaphragm and the piezoelectricelement on the sensor substrate, so that the diaphragm is immersed inthe solution but the piezoelectric element does not immersed in thesolution even if the mass sensor is immersed, so as to install the masssensor on a suitable position. Even if the specimen is a conductivesolution, the electrodes or other parts can be prevented fromshort-circuiting, if the piezoelectric element, the electrodes of thepiezoelectric element and electrode leads connected to the electrode arecoated with a resin or glass insulation coating layer. Furthermore, itis preferable that a shield layer consisting of a conductive material isformed on the surface of said insulation coating layer, so as to reducenoise such as external electromagnetic waves.

[0030] It is preferable that the sensor substrate, diaphragm, connectionplate, sensing plate, and spring plate constituting a mass sensor of thepresent invention are integrally composed of stabilized zirconia orpartially stabilized zirconia. As the material for the piezoelectricfilm in the piezoelectric element, a material containing a componentmainly consisting of lead zirconate, lead titanate, and lead magnesiumniobate is suitably used, oscillation modes, adjusting the resonantfrequencies and sensitivity can be controlled if the shapes of thediaphragm, connection plate, sensing plate, or spring plate aredimensionally adjusted by trimming with laser processing or machining.It is further preferable that the electrode of the piezoelectric elementis laser-processed or machined to adjust the effective electrode area ofthe piezoelectric element.

[0031] The term “piezoelectric” used herein includes piezoelectricityand electric distortion, and what are referred to as a piezoelectricelement include electric distortion elements, and piezoelectric ceramicsinclude electric distortion ceramics.

[0032] Next, according to the present invention, methods for masssensing corresponding to the structure of various mass sensors asdescribed above are provided. First, there is provided a method forsensing the mass with the mass sensor in which a side of at least onesheet-like diaphragm is joined to a side of said sensing plate so thatthe plate surface of said diaphragm is perpendicular to the platesurface of said sensing plate on which a piezoelectric element isinstalled, and the other side of said sensing plate is joined to thesensor substrate, characterized in measuring with said piezoelectricelement resonant frequency on the basis of at least either one of,θ-mode swing oscillation of said diaphragm in which said diaphragm makespendulum-like oscillation centered on the perpendicular axisperpendicularly passing through the center of a fixed plane, which isthe joining surface of said diaphragm and said sensing plate, in thedirection perpendicular to the side of said diaphragm and alsoperpendicular to said perpendicular axis, the φ-mode swing oscillationof said diaphragm in which said diaphragm makes pendulum-likeoscillation centered on said perpendicular axis with the swing in thedirection perpendicular to the side of said diaphragm and alsoperpendicular to said perpendicular axis accompanied by the swing in thedirection parallel to the side of said diaphragm, or the oscillation ofsaid diaphragm in the direction of said perpendicular axis.

[0033] Such a method for mass sensing with a mass sensor is suitablyadopted as a method for mass sensing using the first mass sensoraccording to the present invention as described above from itsstructure.

[0034] Also, according to the present invention there is provided amethod for sensing the mass with the mass sensor having at least onepiezoelectric element, in which a connection plate is joined to adiaphragm at respective sides, at least one sensing plate is joined tosaid connection plate at respective sides in the direction perpendicularto the joining direction of said diaphragm and said connection plate,and at least a part of sides of said connection plate and said sensingplate is joined to a part of sides of the sensor substrate,characterized in measuring with said piezoelectric element resonantfrequency on the basis of at least either one of, the θ-mode swingoscillation of said diaphragm in which said diaphragm makespendulum-like oscillation centered on the perpendicular awnsperpendicularly passing through the center of a fixed plane, which isthe joining surface of said connection plate and said sensor substrate,in the direction perpendicular to the side of said diaphragm and alsoperpendicular to said perpendicular axis, or the φ-mode swingoscillation of said diaphragm in which said diaphragm makespendulum-like oscillation centered on said perpendicular axis with theswing in the direction perpendicular to the side of said diaphragm andalso perpendicular to said perpendicular axis accompanied by the swingin the direction parallel to the side of said diaphragm.

[0035] Such a method for mass sensing with a mass sensor is suitablyadopted as a method for mass sensing using the second and third masssensors according to the present invention as described above from theirstructures.

[0036] Furthermore, according to the present invention there is provideda method for sensing the mass with the mass sensor having at least onepiezoelectric element, in which an assembly of a diaphragm sandwichedwith two connection plates by joining at respective sides is placedacross the side surfaces of a depression or across a through-hole formedon a sensor substrate, at least a plurality of sensing plates are placedbetween said respective connection plates and the bottom side of saiddepression or the side of said through-hole, or between said diaphragmand the bottom side of said depression or the side of said through-hole,in the direction perpendicular to the direction of said respectiveconnection plates sandwiching said diaphragm, characterized in measuringwith said piezoelectric element resonant frequency on the basis of atleast either one of, the θ-mode swing oscillation of said diaphragm inwhich said diaphragm makes pendulum-like oscillation centered on theperpendicular axis perpendicularly passing through the center of a fixedplane, which is the joining surface of said connection plate and saidsensor substrate, in the direction perpendicular to the side of saiddiaphragm and also perpendicular to said perpendicular axis, the φ-modeswing oscillation of said diaphragm in which said diaphragm makespendulum-like oscillation centered on said perpendicular axis with theswing in the direction perpendicular to the side of said diaphragm andalso perpendicular to said perpendicular axis accompanied by the swingin the direction parallel to the side of said diaphragm, the swingoscillation of said diaphragm centered on said perpendicular axis,oscillating in parallel to the direction perpendicular to the side ofsaid diaphragm and also perpendicular to said perpendicular axis, or therotating oscillation of said diaphragm in the plate surface of saiddiaphragm.

[0037] Such a method for mass sensing with a mass sensor is suitablyadopted as a method for mass sensing using the fifth and sixth masssensors according to the present invention as described above from theirstructures, and also suitably adopted as a method for mass sensing usingthe fourth mass sensor having a structure in which the sensing platealso functions as the connection plate.

[0038] According to a mass sensor of the present invention, as describedabove, change in a minute mass occurring in a diaphragm can be knownaccurately in a short time from a specific value of change in theresonant frequencies of the resonating portion provided in the masssensor, and the mass sensor has an advantage of easy measuringoperation. Therefore, by placing the mass sensor in an environmentchanging the resonant frequencies of the resonating portion, variousphysical and chemical quantities can be measured. For example, the masssensor of the present invention can be used suitably as a thicknessmeter for vapor-deposited films and a dew point meter; which utilizedirect change in the mass of the diaphragm, a vacuum meter, viscositymeter, and temperature sensor, which utilize the environment where thediaphragm is placed, such as vacuum, viscosity, and temperature; andespecially, for the identification of a substance to be sensed and themeasurement of its mass by applying to the diaphragm a catchingsubstance which selectively reacts with the substance to be sensed suchas a microorganism or a chemical substance in a specimen, and byutilizing change in the mass of such a catching substance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a perspective view showing an embodiment of a masssensor of the present invention, and (a) through (d) are perspectiveviews of the embodiments in which the location and the number ofdiaphragms are changed;

[0040]FIG. 2 is a perspective view showing an embodiment of apiezoelectric element installed in a mass sensor of the presentinvention;

[0041]FIG. 3 is a perspective view showing an embodiment of anotherpiezoelectric element installed in a mass sensor of the presentinvention;

[0042]FIG. 4 is a perspective view showing an embodiment of stillanother piezoelectric element installed in a mass sensor of the presentinvention;

[0043]FIG. 5 is a diagram showing another embodiment of a mass sensor ofthe present invention; (a) is a plan; (b) is a diagram illustrating aθ-mode swing oscillation; and (c) is a diagram illustrating a φ-modeswing oscillation;

[0044]FIG. 6 is a plan showing still another embodiment of a mass sensorof the present invention;

[0045]FIG. 7 is a diagram showing still another embodiment of a masssensor of the present invention; (a) is a plan; and (b) through (e) aresectional views;

[0046]FIG. 8 is a diagram illustrating the driving of a mass sensor ofthe present invention;

[0047]FIG. 9 is diagram showing still another embodiment of a masssensor of the present invention; (a) and (0) are plans; and (c) is asectional view;

[0048]FIG. 10 is a plan showing still another embodiment of a masssensor of the present invention;

[0049]FIG. 11 is a plan showing the appearance of still anotherembodiment of a mass sensor Of the present invention;

[0050]FIG. 12 is a plan showing the structure of the sensor portion inthe mass sensor shown in FIG. 11;

[0051]FIG. 13 is a perspective view showing the structure of the sensorportion in the mass sensor shown in FIG. 12;

[0052]FIG. 14 is another perspective view showing the structure of thesensor portion in the mass sensor shown in FIG. 12;

[0053]FIG. 15 is a plan showing still another embodiment of a masssensor of the present invention;

[0054]FIG. 16 is a plan showing still another embodiment of a masssensor of the present invention;

[0055]FIG. 17 is a diagram showing still another embodiment of a masssensor of the present invention; (a) is a plan; and (b) is a sectionalview;

[0056]FIG. 18 is a plan showing still another embodiment of a masssensor of the present invention;

[0057]FIG. 19 is a diagram showing still another embodiment of a masssensor of the present invention; (a) is a plan; and (b) through (d) aresectional views;

[0058]FIG. 20 is a plan showing still another embodiment of a masssensor of the present invention;

[0059]FIG. 21 is a plan showing still another embodiment of a masssensor of the present invention;

[0060]FIG. 22 is a diagram showing still another embodiment of a masssensor of the present invention; (a) through (d) and (f) are plansshowing various structures in which a sensing plate is joined toconnection plates; and (e) is a plan showing a structure in which asensing plate is connected to a diaphragm;

[0061]FIG. 23 is a plan showing an example of processing a green sheetfor a sensor substrate used in the fabrication of a mass sensor of thepresent invention;

[0062]FIG. 24 is a diagram illustrating the size and shape which ispreferably adjusted on the fabrication of a mass sensor of the presentinvention;

[0063]FIG. 25 is a diagram illustrating an example of processing apiezoelectric element of a mass sensor of the present invention;

[0064]FIG. 26 is a diagram illustrating operation properties of a masssensor of the present invention;

[0065]FIG. 27 is a sectional view illustrating the basic structure of aconventional micro-mass sensor; and

[0066]FIG. 28 is a perspective view showing the structure of a quartzoscillator of a conventional quartz friction vacuum meter.

BEST MODE FOR CARRYING OUT THE INVENTION

[0067] The embodiments of the present invention will be described belowreferring to drawings, in particular focussing on a mass sensor used byapplying a catching substance that reacts only with a specific substanceto be sensed and catches the specific substance to be sensed to thediaphragm.

[0068] However, since the present invention is not used in many otherapplications as described above, the present invention is not in any waylimited to the embodiments described below.

[0069]FIG. 1(a) is a perspective view showing an embodiment of a masssensor 50A of the present invention. On the plate surface of at leastone sensing plate 51 is provided a piezoelectric element 55 consistingof a first electrode 52, a piezoelectric film 53, and a second electrode54. The piezoelectric element 55 may be provided on both the surfaces ofthe sensing plate 51, and the first and second electrodes 52, 54 areconnected to an electrode lead (not shown) used for connecting them to afrequency meter or the like.

[0070] A sheet-like diaphragm 56 is joined to a side of the sensingplate 51 so that the plate surface of the diaphragm 56 and the platesurface of the sensing plate 51 are perpendicular to each other. Here,“the sides of the sensing plate 51” means a plane perpendicular to theplate surface of the sensing plate 51 on which the piezoelectric element55 is installed, that is, a plane in the thickness direction, and “aside” means one of the sides. Furthermore, the other side of the sensingplate 51, here, the side opposite to the side to which the diaphragm 56is joined, is joined to a sensor substrate 49, and a resonating portionis formed of the diaphragm 56, the sensing plate 51, and thepiezoelectric element 55, to form the mass sensor 50A.

[0071] Here, a diaphragm mainly means the place to cause or to besubject to change in mass, and is an element that oscillates in variousmodes as described later; a connection plate means an element to connectthe diaphragm, sensor substrate, and sensing plate; and a sensing platemeans an element that is deformed by the movement of the diaphragm, andtransmits the strain to the sensing element, such as a piezoelectricelement, installed on the surface, or on the contrary, transmits strainor oscillation generated by a driving element, such as a piezoelectricelement, to the diaphragm. The sensor substrate means an element tosupport the resonating portion, carry various electrode terminals forconnecting to measuring instruments, and is used for handling in actualuses.

[0072] Methods for using such a mass sensor 50A include, for example, amethod in which a catching substance that reacts with and catch only asubstance to be sensed is applied to the diaphragm 56, the diaphragm 56is immersed in a liquid specimen or exposed to a gaseous environmentsuch as a specific gas, to measure change in the resonant frequencies ofthe mass sensor 50A with the piezoelectric element 55, or a method inwhich the resonant frequency is measured after the diaphragm 56 isimmersed in a liquid specimen and dried in a gas. An example of such asubstance to be sensed is an antigen which causes a disease, and anexample of the catching substance is an antibody for such an antigen.

[0073] Here, the resonant frequency of the mass sensor 50A variesdepending on the mass of the resonating portion, in particular, the massof the diaphragm 56. That is, the resonant frequency of the resonatingportion in the state where the substance to be sensed has not beencaught by the diaphragm 56 is different from the resonant frequency ofthe resonating portion in the state where the substance to be sensed hasbeen caught, depending on the mass of the substance to be sensed thathas been caught. Therefore, by measuring change in the resonantfrequencies using the piezoelectric element 55, the mass of thesubstance to be sensed caught by the catching substance applied on thediaphragm 56 can be measured.

[0074] In the same principle, the mass sensor 50A can be used formeasuring decrease in the mass, when the mass of the diaphragm 56decreases from the mass in the initial state. For example, the masssensor 50A can be used suitably when the catching substance applied ispeeled off for some reason, when the extremely slight corrosion or anextremely small amount of dissolution in a specific solution of thematerial itself of the diaphragm 56 is to be checked, or for the purposeto measure change in the mass of a specific chemical substance, otherthan the catching substance, applied to the diaphragm 56 due to theevaporation or dissolution of such a chemical substance.

[0075] The structure of such a mass sensor 50A can be summarized to be astructure in which a side of at least one sheet-Eke diaphragm 56 isjoined to a side of a sensing plate 51 so that the plate surface of thediaphragm 56 is perpendicular to the plate surface on which thepiezoelectric element 55 of the sensing plate 51 is installed, and theother side of the sensing plate 51 is joined to the sensor substrate 49.Here, as the oscillation mode of the diaphragm used for measuringresonant frequency in the mass sensor 50A, it is preferable to measurethe resonant frequency of the resonating portion on the basis of atleast either one of oscillation among θ-mode swing oscillation(hereafter referred to as “θ-mode”) in which the diaphragm 56 performspendulum-like oscillation centered on the perpendicular axis (Y-axis)perpendicularly passing through the center of the fixed plane, which isthe plane where the diaphragm 56 is joined to the sensing plate 51 inFIG. 1(a), in the direction perpendicular to the side of the diaphragm56, and also in the direction perpendicular to the Y-axis, that is inthe direction of X-axis; φ-mode swing oscillation hereafter referred toas “φ-mode”) in which the diaphragm 56 performs pendulum-likeoscillation centered on the Y-axis in the direction perpendicular to theside of the diaphragm 56, and also in the direction perpendicular to theY-axis, that is in the direction of X-axis, and accompanying swingenlarged in the direction parallel to the side of the diaphragm 56(Z-axis) as the diaphragm 56 travels apart from the Y-axis; andoscillation in the direction of the Y-axis.

[0076] These displacement modes mean that the direction of thedisplacement of the diaphragm 56 is dominant in the directions describedabove, but the directional components other than the above directionsare not completely excluded. This applies also to the citation ofdisplacement modes on describing various embodiments below.

[0077] Since these θ-mode and φ-mode are the same as those in the masssensor 30 described later, these will be described in detail in thedescription of the mass sensor 30; however, since these oscillationmodes are the rigid body modes utilizing the side of the diaphragm 56,they are suitably used particularly when the diaphragm 56 or the entiremass sensor 50A is immersed in a liquid.

[0078] When the mass sensor 50A is used in a gas, the bending mode inwhich bending in the direction of Z-axis in FIG. 1(a) is dominant can bealso effectively used in addition to the above oscillation modes. Whenthe bending mode is used in a liquid, although the effect of theviscosity or density of the liquid is larger than in the above θ-modeand φ-mode, change in mass can be known by measuring resonant frequency.Thus, by detecting voltage induced on the piezoelectric film 53 causedby the oscillation of the diaphragm 56 described above, change in theresonant frequency, or change in the mass of the diaphragm 56 can beknown.

[0079] Using the operation principle of the mass sensor 50A describedabove, those shown in FIGS. 1(b) through 1(d) can be exemplified asembodiments on mass sensors having similar function to the embodimentshown in FIG. 1(a). The mass sensor SOB shown in FIG. 1(b) has twoparallel diaphragms 56 similar to the diaphragm 56 in the embodiment ofFIG. 1(a) on a side of the sensing plate 51. The use of a plurality ofdiaphragms 56 can improve the dynamic range of the mass sensor.

[0080] The location where a plurality of diaphragms 56 are joined to thesensing plate 51 is not limited as far as it is a side other than theside where the sensing plate 51 is joined to the sensor substrate 49.Also, since at least one diaphragm 56 is required, the diaphragm 56 maybe joined to the side perpendicular to the side where the sensing plate51 is joined to the sensor substrate 49 among the sides of the sensingplate 51 as in the mass sensor 50C shown in FIG. 1(c). Furthermore, eachof two diaphragms 56 may be joined to a pair of sides opposite to eachother as in the mass sensor 50D shown in FIG. 1(d) to improve dynamicrange as in the mass sensor 50B.

[0081] At this time, it is preferable that the location where thediaphragm 56 is joined to the sensing plate 51 is in the vicinity of theend of the sensing plate 51 apart from the sensor substrate 49 as muchas possible, because the Q-value (peak value, hereafter referred to as“Q-value”) of the θ-mode and φ-mode can be increased, that is, theamplitude of the diaphragm 56 is increased, and the sensitivity isimproved. Of course, the optional combination of these embodiments ofmass sensors 50A-50D shown in FIGS. 1(a) through 1(d) may also be used.

[0082] Although the piezoelectric element 55 installed on mass sensors50A-50D described above is typically of a lamination type in which afirst electrode 52, a piezoelectric film 53, and a second electrode 54are laminated as shown in FIG. 2, a piezoelectric element 62A having acomb structure in which a piezoelectric film 58 is placed on a sensingplate 57 shown in FIG. 3, and a first electrode 59 and a secondelectrode 60 form gaps 61 of a constant width on the top of thepiezoelectric film 58 can also be used. The first electrode 59 and thesecond electrode 60 in FIG. 3 may be formed in the surface between thesensing plate 57 and the piezoelectric film 58. Furthermore, as shown inFIG. 4, a piezoelectric element 62B in which a piezoelectric film 58 isburied between the comb-shaped first and second electrodes 59, 60 isalso suitably used.

[0083] Here, when a comb-shaped electrode as shown in FIGS. 3 or 4 isused, the measuring sensitivity can be raised by reducing the pitch 63.Such piezoelectric elements shown in FIGS. 2 through 4 are used in allthe mass sensors of the present invention described later.

[0084] Although the measurement of mass as described above can beperformed using mass sensors 50A through 50D, increase in detectingsensitivity is limited, because the area of the diaphragm 56 isinevitably small making the area to which a catching substance isapplied small, and making change in mass small when the thickness of thevapor-deposited film is measured. Furthermore, warp or bend may occur onthe diaphragm 56, and in addition, the mode in which only the diaphragm56 oscillates may strongly appear. Therefore, it is preferable to modifythe structure to that shown in FIG. 5(a) to solve such problems.

[0085] That is, FIG. 5(a) is a plan showing another embodiment of a masssensor of the present invention. In the mass sensor 30, a diaphragm 31and a connection plate 33 are joined at their respective sides, and asensing plate 32 is joined to the connection plate 33 at theirrespective sides in the direction perpendicular to the Y-axis direction,which is the direction where the diaphragm 31 and the connection plate33 are joined, that is the X-axis direction. A piezoelectric element 35is installed on at least a part of at least one of the plate surfaces ofthe sensing plate 32 to constitute a sensing portion 36, and at least apart of the sides of the connection plate 33 and the sensing plate 32 isjoined to the side of the sensor substrate 34, without the diaphragm 31being directly joined to the sensor substrate 34. Thus, a resonatingportion is formed of the diaphragm 31, the connection plate 33, thesensing plate 32, and the piezoelectric element 35, to form a masssensor 30.

[0086] Here, although the diaphragm 31, the connection plate 33, and thesensing plate 32 are not necessarily required to have the samethickness, preferably they have the same thickness so as to form thesame surface, and more preferably, they are integrally formed. Theconditions related to the thickness and joining for the diaphragm 31,the connection plate 33, and the sensing plate 32 are likewise appliedto all the mass sensors according to the present invention describedbelow. Furthermore, the sides of the connection plate 33 and the sensingplate 32 are preferably formed integrally with the sensor substrate 34.

[0087] The structure of such a mass sensor 30 can be summarized to be amass sensor having at least one piezoelectric element, in which aconnection plate 33 and a diaphragm 31 are joined together at theirrespective sides; at least one sensing plate 32 is joined to theconnection plate 33 at their respective side in the directionperpendicular to the direction where the diaphragm 31 is joined to theconnection plate 33; and at least a part of the sides of the connectionplate 33 and the sensing plate 32 is joined to a part of the sides ofthe sensor substrate 34. In the mass sensor 30, at least either one ofoscillation modes can be utilized among the bending mode in which thediaphragm 31 oscillates as it bends in the direction of Z-axis (notshown) perpendicular to both X and Y axes; the axial rotation mode inwhich it oscillates as it rotates around the Y-axis; the θ-mode in whichthe diaphragm 31 performs pendulum-like oscillation centered on theY-axis within the plate surface of the diaphragm 31 in the X-axisdirection so as to make a constant angle θ to the Y-axis; and the φ-modewhich is pendulum-like oscillation centered on the Y-axis in the X-axisdirection, and in which the swing component in the direction of theZ-axis (not show-) parallel to the side of the diaphragm 31 is increasedas it travels apart from the Y-axis.

[0088] Here, the above θ-mode and the φ-mode will be described infurther detail. FIG. 5(b) is a diagram illustrating the θ-mode, andshows change in the location of the diaphragm 31 when the mass sensor 30of FIG. 5(a) is viewed from the A-A direction in FIG. 5(a), that is onthe X-axis from the Y-axis direction. Here, the upper end surface 31F ofthe diaphragm 31 is on the location P1 when not oscillating, but in theθ-mode, the diaphragm 31 performs pendulum-like oscillation centered onthe Y-axis within the plate surface of the diaphragm 31, that is, in theX-Y axis plane in the X-axis direction so as to make a constant angle θto the Y-axis. At this time, in the A-A direction, the movement of theupper end surface 31F of the diaphragm 31 can be described as thereciprocal movement between locations P2 and P3 on the X-axis, and thisoscillating movement is defined as the θ-mode.

[0089] Next, FIG. 5(c) is a diagram illustrating the φ-mode, and similarto FIG. 5(b), FIG. 5(c) shows change in the location of the diaphragm 31viewed from the A-A direction shown in FIG. 5(a). Here also, the upperend surface 31F of the diaphragm 31 is on the location P1 when notoscillating. As described above, in the φ-mode, the diaphragm 31performs pendulum-like oscillation centered on the Y-axis within thesurface of the diaphragm 31 in the X-axis direction, and the swingcomponent in the direction of the Z-axis parallel to the side of thediaphragm 31 is increased as it travels apart from the Y-axis. That is,the movement of the upper end surface 31F of the diaphragm 31 in the A-Adirection can be described as the reciprocal movement between locationsP4 and P5 on the arc orbit S having the center O at a point of theZ-axis and passing through location P1. At this time, the angle made bythe Z-axis and the straight line connecting the diaphragm 31 and thecenter O is φ, and such an oscillation mode is defined as the f-mode.

[0090] Due to these various modes of oscillation, the piezoelectric filmof the piezoelectric element 35 is subjected to stretching stress orflexural stress, and a voltage corresponding to the magnitude of thestress is generated. The resonant frequency of the resonating portioncomprising the diaphragm 31, the connection plate 33, and the sensingportion 36 at this time is measured by the piezoelectric element 35.Now, since the resonant frequency of the resonating portion variesmainly accompanying change in the mass of the diaphragm 31, when somesubstance attaches to, or detaches from the diaphragm 31 to cause themass of the diaphragm 31 to change, the change in the mass can beobtained from change in the resonant frequencies of the resonatingportion in the same principle as mass sensors 50A through 50D. Thedynamic range can be increased by installing two piezoelectric elements35 on both surfaces of the sensing plate 32, and by the comparisonoperation of the signals sensed by these piezoelectric elements 35.Furthermore, in this case, sensitivity can be improved by using one ofthe piezoelectric elements 35 for driving (exciting) the diaphragm 31,and the other for sensing (oscillation receiving).

[0091] Further in FIG. 5(a), it is preferable to improve sensitivity, toinstall one piezoelectric element 35 in the Y-axis direction split itinto two piezoelectric element parts 35A and 35B, and use these fordriving and sensing, respectively. The methods for splitting thepiezoelectric element 35 include a method in which after installing onepiezoelectric element 35, it is split by laser processing, and a methodto install two piezoelectric element parts 35A and 35B respectively inthe same time. These methods for installing a plurality of piezoelectricelements, and for splitting and using respective piezoelectric elements35 can be applied to all the mass sensors according to the presentinvention.

[0092] Now, when a resonant frequency is measured by immersing thediaphragm 31 in a liquid utilizing the bending mode described above, thediaphragm 31 has a disadvantage that the diaphragm 31 receivesresistance from the liquid corresponding to the area of the diaphragm31, and becomes difficult to sense change in the minute mass of thediaphragm 31. However, when the specimen is gas, the bending mode can beused because the resistance value is small. In this case, however, it ispreferable to shorten the length of the diaphragm 31 in Y-axis andX-axis directions.

[0093] In the rotation mode around the Y-axis, since change in the massof the diaphragm 31 where the width of the connection plate 33 (width inthe X-axis direction) is extended toward the diaphragm 31, in thevicinity of the Y-axis little affects the rotational oscillation of thediaphragm 31, and less contributes to the rotational oscillation thanthe same change in mass at the left and right ends of the diaphragm 31,a problem arises in sensitivity depending on the location where changein mass of the diaphragm 31 occurs. In this case, measurement error canbe minimized by making the shape of the diaphragm 31 concave, and makingthe area in the vicinity of the Y-axis small like the mass sensor 30A inFIG. 6. At this time, in order to minimize measurement error at thelocation of applying the specimen when change in mass is same, it ispreferable to decrease the dimension H₁; in order to raise the dynamicrange, it is preferable to increase the dimension H₂.

[0094] Whereas, when the θ-mode or the φ-mode is used, no matter whichthe specimen is, liquid or gas, the effect of the location where thecatching substance is applied to the diaphragm 31 can be minimized bydecreasing dimensions H1 and H4 in FIG. 5. In addition, since thediaphragm 31 is thin, the effect of density or viscosity is small, andsince the diaphragm 31 is operated in a rigid body mode, it is littleaffected by temperature change, making the mass sensor excel insensitivity and environment resistance. Therefore, it is preferable tooperate the mass sensor of the present invention in the θ-mode or theφ-mode.

[0095] Next, in the present invention, a structure in which a springplate is bonded in one plate surface or either surface of the connectionplate, and the spring plate is joined to a sensor substrate or a springplate reinforcement can also be adopted favorably. FIG. 7(a) is a planview showing the mass sensor 40A, which is an embodiment in which aspring plate 38 and a spring plate reinforcement 39 are installed on themass sensor 30 described above. FIGS. 7(b) through (e) are varioussectional views on the Y axis viewed from the X-axis direction, showingexamples of the installation of the spring plate 38 and the spring platereinforcement 39.

[0096] The spring plate 38 is joined to at least one plate surface ofthe connection plate 33. Although the width of the spring plate 38 maybe narrower than the width of the connection plate 33 as FIG. 7(a)shows, it is preferable that the width of the spring plate 38 is thesame as the width of the connection plate 33. Also, when spring plates38 made of the same material are bonded on both plate surfaces of theconnection plate 33, it is preferable that the shapes of these springplates 38 are the same. However, when the materials of the spring plates38 are changed on different materials of the connection plate 33, theshapes of these spring plates 38 are not required to be the same, butsuitable shapes may be adopted considering the Young's modulus or otherphysical properties of each spring plate 38.

[0097] Such spring plates 38 are joined also to the sensor substrate 34as a rule. In this case, the necessity of the spring plate reinforcement39 is determined depending on the location where the connection plate 33is joined to the sensor substrate 34. That is, when the connection plate33 is joined to the location where the spring plate 38 is directlyjoined to the sensor substrate 34 as shown in FIGS. 7(b) and (c), nospring plate reinforcement 39 is required, because the sensor substrate34 also functions as the spring plate reinforcement 39. At this time,the spring plate 38 may be bonded only on one plate surface of theconnection plate 33.

[0098] However, when the connection plate 33 is joined to the sensorsubstrate 34 at its end as FIG. 7(d) shows, for the spring plate 38A,the sensor substrate 34 also functions as the spring plate reinforcement39; however, for the spring plate 38B, it is preferable to provide aspring plate reinforcement 39 for supporting the spring plate 38B. Evenwhen the connection plate 33 is joined to the sensor substrate 12 at itsend as FIG. 7(e) shows, no spring plate reinforcement 39 is required ifonly the spring plate 38A which can be joined to the sensor substrate 12is bonded, and no spring plate 38B is used.

[0099] Thus, by bonding the spring plate 38, the mechanical strength ofthe resonating portion is enhanced. Also, by this, the thickness of theconnection plate 33 and the diaphragm 31 can be decreased, and theattenuation of the resonance peak on measurement in a liquid isadvantageously reduced. Furthermore, it is preferable to bond springplates 38 on both plate surfaces of the connection plate 33 because thecenter of gravity of the spring portion consisting of the connectionplate 33 and the spring plates 38 can be excited, and the diaphragm 31oscillates easily in the θ-mode, when exciting the diaphragm 31 with thepiezoelectric element 35.

[0100] Here, sectional views on the X-axis viewed from the Y-axisdirection of the embodiments shown in FIGS. 7(c) and (d) are shown inFIGS. 8(a) and (b), respectively. In FIG. 8(a), since the piezoelectricelement 35 can drive the center O of the spring plate 38A, the springplate 38B, and the connection plate 33 in the X-axis direction, thediaphragm 31 and the whole resonating portion oscillate easily in theθ-mode in the X-axis direction. Whereas, in the case of FIG. 8(b), sincethe center O of the spring plate 38A, the spring plate 38B, and theconnection plate 33 is not on the connection plate 33, the driving forcein the X-axis direction (arrow S₁) by the piezoelectric element 35 isexerted as a rotational force around the center O (arrow S) and therotation mode appears easily, even though the rotation mode isrestricted by the rigidity of the spring plate 38A itself. When thespring plate 38 is used as described above, It is also preferable that areinforcing plate 41 is bonded to the spring plate 38 and joined to theside of the sensor substrate 34, as shown in the mass sensor 40B of FIG.9. FIGS. 9(a) and O) are plans of the mass sensor 40B viewed from thetop and the bottom, respectively; and FIG. 9(c) is a sectional viewalong the X-axis viewed from the Y-axis direction in FIG. 9(b). Here,the reinforcing plate 41 is bonded to the spring plate 38A installed onthe connection plate 33, and joined to the sensor substrate 34 at theperpendicularly cut side. Preferably, the reinforcing plate 41 isintegrally formed with the sprig plate 38 and the sensor substrate 34.

[0101] Since such a structure facilitates the diaphragm 31 to resonatein the θ-mode and the φ-mode, the attenuation of the Q value is reduced,and sensitivity is advantageously improved Therefore, the structure issuitable particularly for measurement in liquid.

[0102] Obviously, the spring plate described above can be applied to allthe mass sensors according to the present invention in which aconnection plate is used as a component, and it is preferable that thespring plate is integrally formed with an intermediate plate integrallyinserted between the diaphragm plate and the base plate, or integrallyformed with a spring plate reinforcement which has been integrallyformed with the diaphragm, and also integrally formed with respectiveconnection plates as described later in the method for manufacturing themass sensor of the present invention.

[0103] The shape of the plate surface of the diaphragm 31 in the abovemass sensor 30 is not limited to rectangular as shown in FIG. 5(a), FIG.7(a), and FIG. 9, but various optional shapes, such as circulartriangular, inverted U-shape, polygonal, ellipse, and oval, as shown inmass sensors 30B through 30D of FIGS. 10(a) through (c), may be used.The diaphragm 31 may be not joined to the connection plate 33symmetrically about the Y-axis, as shown in the mass sensor 30E of FIG.10(d). Such an optional selection of the shape of the diaphragm 31 canalso be applied to all the mass sensors of the present invention.

[0104] Next, an embodiment of a mass sensor in which only one springplate is bonded to the mass sensor 30 described above, and is assembledin the sensor substrate is shown in FIG. 11. In the mass sensor 1, it isobviously possible to form the spring plate, spring plate reinforcement,and reinforcing plate described above, or to change the shape of thediaphragm optionally.

[0105]FIG. 11 is a plan of a mass sensor 1 viewed from the direction ofthe diaphragm 3. The mass sensor 1 is designed to be symmetrical. Theoscillation plate 3 constitutes the sensor substrate 2 together with thebase plate 15 and the intermediate plate 17 as described later. Holes 8formed in the sensor substrate 2 are used as alignment marks utilized inpackaging and manufacturing processes of the mass sensor 1, and tworesonating portions 26, one of which is used for referencing, consistingof a diaphragm 19, a connection plate 20, a sensing plate 21, apiezoelectric element 25, and a spring plate 18 as described later areformed. By forming two or more resonating portions 26 in one mass sensor1, including a resonating portion 26 for referencing, signals fromrespective resonating portions 26 can be cumulated to expand the dynamicrange.

[0106] The position sensor electrodes a, 5 are used or sensing theposition of the mass sensor 1 when the mass sensor 1 is immersed in aconductive specimen such as an aqueous solution by conducting anelectric current through the specimen. When the specimen is conductive,these position sensor electrodes 4, 5 prevent the second electrode 24and the first electrode 22 on the piezoelectric element 25 (not shown inFIG. 11), and electrode leads 9, 10 from these electrodes fromshort-circuiting, by making the part above the pattern formed in thehorizontal direction of the position sensor electrodes 4, 5 immersed inthe specimen, and making the part of the mass sensor 1 deeper than theposition the position sensor electrodes 4, 5 sensed not immersed in thespecimen. To an end of each of the position sensor electrodes 4, 5 isformed a terminal 6, 7, respectively; and to an end of each of theelectrode leads 9, 10 is formed a terminal 11, 12, respectively. Theseterminals are connected to the probes or other connectors on respectivesensor instruments.

[0107] However, when the piezoelectric element 25 and the electrodeleads 9, 10 are coated with an insulating resin or the like, since thesepiezoelectric element 25 and electrode leads 9, 10 are notshort-circuited even if the mass sensor 1 is immersed in the conductivespecimen, no position sensors 4, 5, and terminals 6, 7 are required.

[0108]FIG. 12 is an enlarged plan showing the sensor portion 13 in FIG.11 viewed from the base plate 15, that is, viewed from the back side ofthe oscillation plate 3 in FIG. 11. FIG. 13 is a perspective viewshowing the vicinity of the cut portion 16 shown in FIG. 12. The sensorportion 13 means a portion of the mass sensor 1, comprising theresonating portion 26 and the sensor substrate 2 in the vicinity of theresonating portion 26 in the mass sensor 1.

[0109] As FIGS. 12 and 13 show, an opening 14 having U-shaped cutportion 16 is formed in the base plate 15. The same shape of cut portion16 is also formed on the intermediate place 17 overlapping the baseplate 15, and in the intermediate place 17, an almost prismatic springplate 18 extending toward the center of the opening 14 from the centerof the bottom side of the cut portion 16 is formed. However, theseintermediate plate 17 and the spring plate 18 are not always required,but are used as the members constituting the mass sensor 1 when requiredfor the adjustment of the mechanical strength of the resonating portion26 or the sensitivity of the mass sensor 1.

[0110] In the cut portion 16 of the oscillation plate 3 are formed aconnection plate 20 joined to the spring plate 18, and a diaphragm 19joined to the upper end of the connection plate 20, but not joined tothe spring plate 18. Furthermore, in the cut portion 16 of theoscillation plate 3, a sensing plate 21 is formed across a side of theconnection plate 20 and the facing side of the cut portion 16.

[0111]FIG. 14 shows a perspective view of the vicinity of the cutportion 16 shown in FIG. 12 viewed from the oscillation plate 3 side. Onthe surface of the oscillation plate 3 side of the sensing plate 21 isformed a piezoelectric element 25 by laminating a first electrode 22, apiezoelectric film 23, and a second electrode 24 in this order.Furthermore, the second electrode 24 is connected to the electrode lead9, and the first electrode 22 is connected to the electrode lead 10.Thus, a sensing portion 29 is constituted of the sensing plate 21 andthe piezoelectric element 25, and the resonating portion 26 isconstituted of the spring plate 18, the diaphragm 19, connection plate20, and the sensing portion 29.

[0112] Although only a piezoelectric element 25 is installed on oneplate surface of the sensing plate 21 in the mass sensor 1,piezoelectric elements 25 may be installed on both plate surfaces of thesensing plate 21. In this case, since the structure of the sensingportion 29 becomes symmetrical, the rigidity of the sensing plates 21can be equalized.

[0113] Also in the mass sensor 1, although a slit 27 is formed on thelower edge of the cut portion 16 in the sensing plate 21 and theoscillation plate 3 as FIG. 13 shows, it is preferable that a structurein which the sensing plate 21 is joined to the lower edge of the cutportion 16 in the oscillation plate 3 without forming the slit 27, thatis, the sensing plate 21 is fitted in and joined to the depressionformed by the connection plate 20 and the sensor substrate 2 as in themass sensor 42 shown in FIG. 15, to restrict the bend of the springportion consisting of a connection plate 20 and/or a spring plate 18,and to increase the stress applied to the piezoelectric element 25.

[0114] In the mass sensor 1 described above, although a sensor portion13 is installed utilizing the circumference of the opening 14 formed inthe sensor substrate 2, the sensor portion 13 may be installed on thecircumference of the sensor substrate 2, for example, on the upper edgein FIG. 11. However, since the sheet-like diaphragm 19 is ofteninstalled on the location projected from the cut portion 16, as obviousfrom the structure of the sensor portion 13 shown in FIGS. 11 through14, it is preferable to adopt the structure in which the sensor portion13 is installed inside the sensor substrate 2 as FIG. 11 shows,considering the protection of the resonating portion 26 from externalimpact, for example, so as not to damage the diaphragm 19 on handlingthe mass sensor 1. Such a structure is also preferable for facilitatingthe manufacturing process of the mass sensor 1 as will be describedlater.

[0115] Next, various embodiments of mass sensors that can substitute thesensor portion 13 in the mass sensor 1 described above will bedescribed. FIG. 16(a) is a plan showing a mass sensor 43A, which isanother embodiment of the present invention. The mass sensor 43A has thestructure in which a connection plate 20 and a diaphragm 19 are joinedtogether at the respective sides, two sensing plates 21A, 21B are joinedto the connection plate 20 so as to sandwich the connection plate 20 inthe direction perpendicular to the direction where the diaphragm 19 andthe connection plate 20 are joined, and respective sensing plates 21A,21B are also joined to the sensor substrate 2 in the same way as thesensing plate 21 in the mass sensor 42 shown in FIG. 15 and supportedand fixed at three sides. This three-side supporting is intended toelevate sensitivity. However, the sensing plates 2 1A, 2 1B are notnecessarily required to be joined to the lower edge of the depressionformed by the connection plate 20 and the sensor substrate 2.

[0116] Piezoelectric elements each consisting of a first electrode, apiezoelectric film, and a second electrode are installed on at least apart of at least one of plate surfaces of at least one of sensingplates. In the embodiments shown in FIG. 16, piezoelectric elements 25Athrough 25D are installed on both plate surfaces of sensing plates 21A,21B, and the resonating portion is formed of a diaphragm 19, aconnection plate 20, the sensing plates 21A, 21B, and the piezoelectricelements 25A through 25D. However, all the piezoelectric elements 25Athrough 25D are not necessarily required, but the optional number of thepiezoelectric elements may be installed on optional locations of thesensing plate 21A or 21B.

[0117] When a plurality of piezoelectric elements 25A through 25D areused as in this mass sensor 43A, since the rigidity of the sensingplates 21A and 21B can be equalized, and in addition, the Q values inthe θ-mode and the φ-mode can be increased and the Q value of therotation mode can be decreased by cumulating or processing signals fromthe respective piezoelectric elements 25A through 25D, resonantfrequencies can be measured more accurately. Furthermore, when at leasttwo of the piezoelectric elements 25A through 25D are installed, if oneis used for driving and the other is used for sensing, sensitivity canbe improved. Here, it is preferable for improving sensitivity to splitthese piezoelectric elements 25A through 25D in the similar way as thepiezoelectric element 35 is split into piezoelectric elements 35A and35B in the mass sensor 30.

[0118] It is also preferable for improving output charge to adopt thestructure in which, for example, piezoelectric elements 25A and 25C areinstalled on the plate surfaces in the same orientation of sensingplates 21A and 21B, respectively, and the polarizing direction of thepiezoelectric films in these piezoelectric elements 25A and 25C isreversed to each other. It is also preferable to adopt such a structureon respective plate surfaces of the sensing plates 21A and 21B.Furthermore, it is preferable for improving sensitivity to adopt thestructure in which at least one of directions of at least one of thepiezoelectric elements 25A through 25D, for example, the piezoelectricelements 25C and 25D is a side or two sides of three-side supporting asin the mass sensor 43B shown in FIG. 16(b). Even in this case, however,it is required that the piezoelectric elements 25A through 25D do notoverlap the spring plate when the connection plate 20 and the springplate are used.

[0119] When spring plates are bonded to mass sensors 43A, 43B, springplate reinforcements or reinforcing plates can be used as in the masssensor 40B. For example, a reinforcing plate is formed so that it isbonded to a spring plate, and the side of the reinforcing plate isjoined to three sides, that is, the sides of the sensor substrate 2where the sensing plates 21A, 21B, are joined to the sensor substrate 2(the lateral side of the cut portion 16), and the side of the sensorsubstrate 2 where the connection plate 20 is joined to the sensorsubstrate 2 (the bottom side of the cut portion 16). This is preferablefor improving sensitivity, because the Q value in the θ-mode can beimproved, the resonant frequency in the flexural mode (the mode bendingbetween the sensor substrate and the connection plate) of thepiezoelectric element can be increased, and the frequency in the θ-modecan be increased.

[0120] The mass sensor 43C shown in FIG. 16(c) is an embodiment in whicha slit 48 is formed on the center in the length direction of theconnection plate 20 in the mass sensor 43A. The slit 48 is hollow, andhas functions to facilitate oscillation in the θ-mode and the φ-mode ofthe diaphragm 19 to occur, and the resonant frequency to be identified.Also, as described later, the slit 48 has functions to reduce the massof the connection plate 20 and to improve sensitivity. When a springplate is used, the spring plate may be formed in the shape having such ahollow, and integrated with the connection plate.

[0121] When two sensing plates are installed on one resonating portionas shown in FIG. 16(a), the driving force of the diaphragm 19 can beincreased by expanding the area of either one of the sensing plates 21Aand 21B by changing the lengths N₁ and N₂ and the widths M₁ and M₂ ofthe sensing plates 21A and 21B, and the Q values in the θ-mode and theφ-mode can be increased by narrowing the area of the other sensingplate, as FIG. 17(a) shows. FIG. 17(b) is a sectional view along theX-axis of FIG. 17(a) viewed from the Y-axis direction. The Q values inthe θ-mode and the φ-mode can be increased or sensitivity is improved bychanging the natural frequency of the bending displacement oscillationof the sensing plates 21A, 21B determined by the piezoelectric elements25A, 25B and the sensing plates 21A, 21B (arrow G in FIG. 17(b)) to f₁and f₂, respectively, by changing the widths M₁ and M₂ of the sensingplates 21A, 21B, for example, by using one of the piezoelectric elements25A, 25B for driving and the other for sensing. Also, the piezoelectricelement having either smaller natural frequencies f₁ and f₂ may be usedfor driving, and the other may be used for failure diagnosing.

[0122] When two sensing plates are used in one resonating portion asshown in FIG. 16 or 17, it is also preferable to adopt a structure inwhich at least one of the piezoelectric elements 25C, 25D is installedon one sensing plate, for example, the sensing plate 21B, and a slit 28is formed on the other sensing plate 21A in the direction perpendicularto the direction where the sensing plate 21A is joined to the connectionplate 20 as FIG. 18 shows. By such a structure, the oscillation in therotation mode can be restricted, the Q values in the θ-mode and theφ-mode can be increased, and the deviation of the resonance point can beincreased to increase the absolute value of the variation of resonantfrequencies. Although the number of the slit 28 may be one, a pluralityof slits are preferable to enhance the effects mentioned above.

[0123] Next, FIG. 19(a) shows a plan of a mass sensor 43D, an embodimentin which the mass sensor 43A shown in FIG. 16(a) is formed in theopening 14 formed in the sensor substrate 2; FIG. 19(b) shows asectional view thereof along the broken line A-A in FIG. 19(a). In themass sensor 43D, two piezoelectric elements 25A, 25C are installed, andelectrode leads 9, 10 are connected to the piezoelectric elements 25A,25C, respectively. An insulation coating layer 65 is formed to cover thepiezoelectric elements 25A, 25C and the electrode leads 9, 10. Thisinsulation coating layer 65 protects the piezoelectric elements 25A, 25Cand the electrode leads 9, 10 from short-circuiting even if theresonating portion of the mass sensor 43D is immersed in a conductivespecimen.

[0124] The mass sensor 43D is also provided with shield layers 66comprising a conductive material so as to cover the insulation coatinglayer 65. The shield layer 66 are formed on both tile surfaces of thesensor substrate 2 and connected to each other through a through-hole67. When sensing an extremely small mass of the 0.1 ng order, it ispreferable to also shield the wiring members (piezoelectric elements25A, 25C and electrode leads 9, 10) on the sensor substrate 2, as wellas the wiring from the sensor substrate 2 to the instrument, in order toshield the mass sensor from external electromagnetic waves and tominimize the determination error of resonant frequencies.

[0125] In addition to the aspect of the formation of the shield layer 66so as to sandwich the sensor substrate 2 as shown in FIG. 19(b), theembodiment in which the shield layer surround only the wiring members onthe sensor substrate 2 as shown in the sectional view of FIG. 19(c), andthe embodiment in which a shield layer covers only the upper side of thewiring members as shown in FIG. 19(d) may also be used. Particularly,the embodiments to shield the entire wiring members as shown in FIGS.19(b) and (c) are preferable. In the embodiment of FIG. 19(a), althoughthe shield layer 66 formed on both the surfaces of the sensor substrate2 are electrically connected to each other through the through-hole 67,these layers may be connected by utilizing the side of the sensorsubstrate 2. The detail of the materials favorably used for theformation of the insulation coating layer 65 and the shield layer 66will be described later together with the description of materials usedin the mass sensors.

[0126]FIG. 20 is plan showing another embodiment of a mass sensor of thepresent invention. In the mass sensor 44A shown in FIG. 20(a), aconnection plate 20 is not directly joined to a sensing plate 21, butthe connection plate 20 and the sensing plate 2i are connected to adiaphragm 19 at respective sides so that the directions of joining tothe diaphragm 19 are in parallel to each other, and the diaphragm 19 isnot joined to the sensor substrate 2, but the connection plate 20 andthe sensing plate 21 are connected to the side of the sensor substrate2. That is, the sensing plate 21 also functions as the connection plate20.

[0127] A piezoelectric element 25 is installed on at least a part of atleast one of the plate surfaces of the sensing plate 21, and theresonating portion is formed of the diaphragm 19, the connection plate20, the sensing plate 21, and the piezoelectric element 25. Whereas, inthe mass sensor 44B shown in FIG. 20(b), two sensing plates 21A, 21B areformed on both the sides of a connection plate 20, and piezoelectricelements 25A, 25B are installed on the sensing plates 21A, 21B,respectively.

[0128] Such mass sensors 44A, 44B are suitable for measurement in the0mode, because the oscillation of the diaphragm 19 easily occurs in theplane of the diaphragm 19, and the oscillation of the diaphragm 19 inthe rotation mode is restricted. Since the oscillation of the diaphragm19 is directly transmitted to the piezoelectric element 25 through thesensing plates, the sensitivity of the mass sensors is advantageouslyimproved.

[0129] Next, FIGS. 21(a) through (c) are plans showing still anotherembodiment of the mass sensor of the present invention. First, in themass sensor 45A shown in FIG. 21(a), a diaphragm 72 is joined to twoconnection plates 74A, 74B at respective sides so that the connectionplates 74A, 74B sandwich the diaphragm 72, and the connection plates74A, 74B bridge across the side walls of the depression 76 of the sensorsubstrate 70 at respective sides. Here, the depression 76 has a similarfunction as the cut portion 16 formed in the mass sensor 1, andtherefore, may be formed on the side or other portions of the sensorsubstrate 70 similarly to the circumference of the sensor substrate 2shown in FIG. 11 or the opening 14 formed in the sensor substrate 2.

[0130] The sensing plates 73A, 73B are provided across the connectionplates 74A, 74B and the bottom of the depression 76 in the directionwhere connection plates 74A, 74B sandwich the diaphragm 72, that is, inthe direction perpendicular to the Y-axis direction. Furthermore,piezoelectric elements 75A, 75B are installed on at least one of theplate surfaces of the sensing plates 73A, 73B, respectively. Thus aresonating portion is formed of the diaphragm 72, connection plates 74A,74B, sensing plates 73A, 73B, and piezoelectric elements 75A, 75B.

[0131] The structure of the mass sensor 45A can be summarized as a masssensor having at least one piezoelectric element, in which a diaphragm72 is sandwiched by and joined to two connection plates at respectivesides, the connection plates 74A, 74B bridge across the side walls ofthe opening or gap formed in the sensor substrate 70, and at least aplurality of sensing plates 73A, 73B are provided across the connectionplates 74A, 74B and the sides of the opening or gap in the directionperpendicular to the direction where the respective connection plates74A, 74B sandwich the diaphragm 72.

[0132] In such a mass sensor 45A, the resonant frequency of theresonating portion on the basis of at least some of, the θ-mode swingoscillation in which the diaphragm 72 performs pendulum-like oscillationon the fixed surface where respective connection plates 74A, 74B arejoined to the sensor substrate 70, centered on the perpendicular axiswhere the diaphragm 72 perpendicularly passes through the fixed surface,that is the Y-axis, and in the direction perpendicular to the side ofthe diaphragm 72 and perpendicular to the Y-axis, that is the X-axis;the φ-mode swing oscillation in which the diaphragm 72 performspendulum-like oscillation centered on the Y-axis in the X-axis directionaccompanying the swing in the direction parallel to the side of thediaphragm 72, that is the Z-axis (not shown); swing oscillation in whichthe diaphragm 72 performs oscillation centered on the Y-axis in theX-axis direction; or rotational oscillation in the plate surface of thediaphragm 72; can be measured by the piezoelectric elements 75A, 75Binstalled on the sensing plates 73A, 73B.

[0133] The structures of mass sensors 46A through 46F described latercan also be summarized similarly to the mass sensors 45A through 45C,and the method for mass sensing with the mass sensors 46A through 46F isthe same as that of the mass sensors 45A through 45C. However, in themass sensors 46A through 46F, the number of the sensing plates isincreased to four, and in these embodiments, there is added thestructure in which at least a plurality of sensing plates 73A through73D bridge between the diaphragm 72 and the side of the opening or gapin the direction perpendicular to the direction where respectiveconnection plates 74A, 74B sandwich the diaphragm 72.

[0134] Therefore, since the diaphragm 72 and the sensing plates 73A, 73Bare oscillated in the direction of arrow K in FIG. 21, that is, makingthe Y-axis the center of oscillation, and the direction parallel to theplate surface of the diaphragm 72 and also perpendicular to the Y-axis,that is the X-axis direction, the diaphragm 72 oscillates in thedirection of arrow K stably in the rigid body mode as the θ-mode of thediaphragm 72. There is also an advantage that the flexural mode of thediaphragm 72 is restricted. The shape of the diaphragm 72 is not limitedto rectangular as shown in FIGS. 21(a) through (c), but optional shapesas shown in FIG. 10 can be adopted, and as in the mass sensor 45B shownin FIG. 21(b), the diaphragm 72 may be joined to respective connectionplates 74A, 74B at optional locations. Furthermore, as in the masssensor 45C shown in FIG. 21(c), the respective sensing plates 73A, 73Bmay be supported and fixed at three sides by the respective connectionplates 74A, 74B and the sensor substrate 70 in the same way as thesensing plate 21 in the mass sensor 42 shown in FIG. 15. In the masssensor 45B, a position sensor 77 similar to the position sensors 4,5 ofthe mass sensor 1 is installed.

[0135] Next, in mass sensors 46A through 46F, still other embodiments ofthe present invention shown in the plan of FIGS. 22(a) through (f), adiaphragm 72 is sandwiched by and joined to two connection plates 74A,74B at respective sides, the respective connection plates 74A, 74Bbridge across the side walls of the opening 71 of the sensor substrate70, and at least a plurality of sensing plates, here sensing plates 73Athrough 73D, are provided between the respective connection plates 74A,74B and the side wall of the opening 71, or between the diaphragm 72 andthe side wall of the opening 71 in the direction perpendicular to thedirection where the connection plates 74A, 74B sandwich the diaphragm72.

[0136] Furthermore, piezoelectric elements 75A through 75D are installedon at least one of the plate surfaces of at least one of the sensingplates 73A through 73D, and thus a resonating portion is formed of adiaphragm 72, connection plates 74A, 74B, sensing plates 73A through73D, and piezoelectric elements 75A through 75D.

[0137] When mass sensors 46A through 46F shown in FIGS. 22(a) through(f) are seen, in the mass sensor 46A shown in FIG. 22(a), rotation ofthe diaphragm 72 about the Y-axis is restricted by the sensing plates73A, 73B compared with the structures of mass sensors 45A through 45Cshown in FIG. 21. It is preferable to form slits 28 on the sensingplates 73A, 73B as in the embodiment shown in FIG. 17 because thediaphragm 72 oscillates easily in the direction of arrow K.

[0138] In the mass sensor 46B of FIG. 22(b), piezoelectric elements 75Athrough 75D are installed on the surfaces of all of the sensing plates73A through 73D shown in FIG. 22(a) oriented to the same direction. Bythis, the amplitude of the diaphragm 72 oscillating in the K directionis increased, and the mass sensor can be suitably used for themeasurement in high viscous substances as well as in low viscoussubstances. At this time, the direction of the polarization ofpiezoelectric films of the piezoelectric elements 75A and 75C, and 75Band 75D should be opposite to each other. Furthermore, the piezoelectricelements 75A through 75D may be installed on both sides of the sensingplates 73A through 73D.

[0139]FIG. 22(c) shows a mass sensor 46C in which a side of sensingplates 73A through 73D in the embodiments shown-r in FIGS. 22(a) and go)facing to the sensor substrate 70 is joined to the sensor substrate 70.By such a structure, the effects obtained by the structure of the masssensor 42 shown in FIG. 15 can be added to the effects of theembodiments shown in FIGS. 22 (a) and (b).

[0140] In the mass sensor 46D of FIG. 22(d), piezoelectric elements 75B,75C are installed on the sensing plates 73B, 73C locatedpoint-symmetrically about the intersection of the X-axis and the Y-axis,which is the center of the diaphragm 72. Since the resonant frequency issensed using the rigid body mode in which oscillation in the η directionaround the intersection of the X-axis and the Y-axis (direction of thearrow in FIG. 22(d)) is dominant, the sensing plates 73A, 73D are notnecessarily required. When the sensing plates 73A, 73D are formed, slitsor piezoelectric elements 75A, 75D may be provided on the sensing plates73A, 73D. In this case, it is preferable that the directions ofpolarization of respective piezoelectric films in each set of thepiezoelectric elements 75A and 75D, and 75B and 75C are the same.

[0141] In the mass sensor 46E of FIG. 22(e), sensing plates 73A through73D are joined to the diaphragm 72, and the locations of thepiezoelectric elements 75A through 75D are the same as in the case ofFIG. 22(b). The oscillation of the diaphragm 72 in the direction ofarrow K can also be sensed by such a structure. Furthermore, the masssensor 46F shown in FIG. 22 (f) has the structure which oscillateseasily in the θ-mode and the φ-mode by increasing the width of eitherone of the connection plates 74A, 74B, and decreasing the width of theother.

[0142] Thus, although various shapes can be selected in the mass sensorsof the present invention, materials used for producing these masssensors are not changed depending on respective mass sensors. Then,members constituting a mass sensor of the present invention and theirshapes will be described using the mass sensor 1 described above. First,the sensor substrate 2, diaphragm 19, connection plate 20, sensing plate21, and spring plate 18 are preferably made of ceramics, for example,stabilized or partially stabilized zirconia, alumina, magnesia, orsilicon nitride. Among these, stabilized or partially stabilizedzirconia is most preferably used because they have a high mechanicalstrength even in case of a thin plate, a high toughness, and a lowreactivity with the materials of piezoelectric films or electrodes.

[0143] When stabilized or partially stabilized zirconia mentioned aboveis used as the material for the sensor substrate 2, it is preferable toadd an additive such as alumina and titania at least to the sensingplate.

[0144] Although the oscillation plate 3, intermediate plate 17, and baseplate 15 in the sensor substrate 2, and the diaphragm 19, connectionplate 20, spring plate 18, and sensing plate 21 are not necessarilyrequired to be composed of the same material, and various ceramicmaterials may be used in combination depending on the design, it ispreferable to constitute these members integrally using the samematerial from the point of view of the reliability of the parts wherethese members are joined, and the simplification of the manufacturingprocess.

[0145] However, when the spring plates 18 are formed on both the platesurfaces of a connection plate 20, the spring plate formed on thesurface on which a piezoelectric element 25 is installed can be producedto have the same structure as the piezoelectric element 25. This ispreferable for the manufacturing process, since the spring plate can beformed simultaneously with the piezoelectric element 25. However, forthe piezoelectric element formed as a spring plate, the electrode is notused as the electrode.

[0146] Although major purpose of the mass sensor 1 is sensing a mass ofthe 0.1 nanogram (ng) order, the thickness of the diaphragm 19 ispreferably about 3 to 20 μm, more preferably about 5 to 15 μm, and thethickness of the base plate 15 is suitably determined considering theease of operation.

[0147] When a spring plate 18 is formed, in either case where it isbonded on one side or on both sides of the connection plate 20, thethickness is preferably 10 to 220 μm, the width is preferably 100 to 500μm, and the aspect ratio (width/thickness) of the spring plate 18 ispreferably in a range between 0.4 and 50. When the attenuation ofoscillation amplitude by the use of the mass sensor 1 in a liquid isconsidered, the thickness is preferably 10 to 70 μm, the width ispreferably 100 to 500 μm, and the aspect ratio is preferably 1.4 to 50.More preferably, the thickness is 10 to 70 μm, the width is 100 to 300μm, and the aspect ratio is 1.4 to 30. The thickness of the spring platereinforcement, when such a spring plate reinforcement is required, ispreferably the same as the thickness of the spring plate being joined tothe spring plate reinforcement.

[0148] Whereas, the connection plate 20 may be used as a spring platewithout forming the spring plate 18. In this case, no intermediate plate17 may be formed, but it is preferable to increase the thickness of thebase plate 15 by the thickness of the intermediate plate 17 formaintaining the mechanical strength of the sensor substrate 2.

[0149] For the piezoelectric film 23 in the piezoelectric element 25,although film-like piezoelectric ceramics are suitably used,electrostriction ceramics or ferroelectric ceramics may also be used.Such materials may be either those requiring or not requiringpolarization.

[0150] Ceramics that can be used in the piezoelectric film 23 include,for example, lead zirconate, lead titanate, lead magnesium niobate, leadnickel niobate, lead zinc niobate, lead manganese niobate, lead antimonystannate, lead manganese tungstate, lead cobalt niobate, and bariumtitanate. These may be used alone, or as ceramics containing thecombination of some of them. In the present invention, a materialcontaining the components consisting mainly of lead zirconate, leadtitanate, and lead magnesium niobate as the main component is preferablyused, because such a material not only has high electrical-mechanicalcoupling coefficient and piezoelectric constant, but also has smallreactivity with the sensor substrate member on sintering piezoelectricfilm, and can form the desired composition stably.

[0151] Furthermore, ceramics containing the oxides of lanthanum,calcium, strontium, molybdenum, tungsten, barium, niobium, zinc, nickel,manganese, cerium, cadmium, chromium, cobalt, antimony, iron, yttrium,tantalum, lithium, bismuth, and tin alone, or in the combination of someof these oxides, or ceramics in which other compounds of these elementsare added may be used for the above piezoelectric ceramics. For example,a ceramic material containing lead zirconate, lead titanate, and leadmagnesium niobate as main components, to which lanthanum or strontium isadded is also preferable, and such a material to which manganese isfurther added is preferable because the mechanical quality factor islarge, and the Q value can be increased not only from the structure ofthe sensor but also from the material.

[0152] On the other hand, the first electrode 22 and the secondelectrode 24 in the piezoelectric element 25 are preferably formed froma metal that is solid at room temperature and conductive. For example, ametal such as aluminum, titanium, chromium, iron, cobalt, nickel,copper, zinc, niobium, molybdenum, ruthenium, palladium, rhodium,silver, tin, tantalum, tungsten, iridium, platinum, gold, or lead alone,or an alloy of some of these elements can be used. Furthermore, a cermetmaterial in which the same material used in the piezoelectric film 23 orthe sensing plate 21 is dispersed in these materials may be used.

[0153] The selection of the material for the actual first electrode 22and the second electrode 24 is determined depending on the method forforming the piezoelectric film 23. For example, when the first electrode22 is formed on the sensing plate 21, then the piezoelectric film 23 isformed on the first electrode 22 by sintering, the first electrode 22must be made of a high melting point metal, such as platinum, which isnot affected by the temperature for sintering the piezoelectric film 23.However, since the second electrode formed on the piezoelectric film 23after forming the piezoelectric film 23 can be formed at a lowtemperature, a low melting point metal, such as aluminum, can be used.

[0154] Although the piezoelectric element 25 can be formed integrally bysintering, in this case, both the first electrode 22 and the secondelectrode 24 must be made of a high melting point metal which resiststhe temperature for sintering the piezoelectric film 23. On the otherhand, when the first and second electrodes 59, 60 are formed on thepiezoelectric film 58 after forming the piezoelectric film 58, as in thepiezoelectric element 62A shown in FIG. 3, both electrodes can be madeof the same low melting point metal, but when the piezoelectric element62A is simultaneously sintered, both the first electrode 22 and thesecond electrode 24 must be made of a high melting point metal. Thus,the materials for the first electrode 22 and the second electrode 24 canbe selected suitably depending on the temperature for forming thepiezoelectric film 23 represented by the sintering temperature of thepiezoelectric film 23, and the structure of the piezoelectric element25. The materials and methods for forming the electrode leads 9, 10 arethe same as those for the first electrode 22 and the second electrode 24of the piezoelectric element 25.

[0155] Since a problem arises when the area of the piezoelectric film 23is expanded, in that although sensitivity increases because of increasein the output charge, the size of the sensor increases, the area of thepiezoelectric film 23 should be designed to an adequate size. Also,since a problem arises when the thickness of the piezoelectric film 23is decreased, in that although sensitivity increases, the rigidity ofthe piezoelectric film 23 is lowered, the total thickness of the sensingplate 21 and the piezoelectric film 23 is preferably 15 to 50 μm.

[0156] When an insulation coating layer 65 is formed on thepiezoelectric element 25 and the electrode leads 9, 10 as in the masssensor 43D shown in FIG. 19, insulating glass or resin is used as itsmaterial. For enhancing the performance of the mass sensor 1, a resin ismore preferably used as the material for the insulation coating layerthan glass, and chemically stable fluorine resins, for example,tetrafluoroethylene-based Teflon (Teflon PTFE of DuPont),tetrafluoroethylene-hexafluoropropylene copolymer-based Teflon (TeflonFEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer-basedTeflon (Teflon PFA), and PTFE/PFA composite Teflon are preferably used.Although corrosion resistance and weather resistance are lower thanthose of these fluorine resins, silicone resins (in particular,thermosetting silicone resins) can be suitably used, and epoxy resins oracrylate resins can also be used depending on the applications. It isalso preferable to form the insulation coating layer 65 using differentmaterials for the piezoelectric element 25 and its vicinity, and theelectrode leads 9, 10 and their vicinity. Furthermore, it is alsopreferable to add inorganic or organic fillers in the insulating resinto adjust the rigidity of the resonating portion.

[0157] When the insulation coating layer 65 is formed, the materials fora shield layer 66 formed on the insulation coating layer 65 arepreferably metals such as gold, silver, copper, nickel, and aluminum;however, any metallic materials used in the first electrode 22 of thepiezoelectric element 25 or the like described above can be used. Aconductive paste comprising metal powder mixed in a resin may also beused.

[0158] Next, the method for using a mass sensor of the present inventionwill be described when the mass sensor 1 is used as an immune sensor.One of two sensor portions 13 is used as a detection sensor portion 13D.To the diaphragm of the detection sensor portion 13D is applied acatching substance which reacts with only a substance to be sensed, suchas a pathogenic virus, and catches it. For example, the combination ofan antigen as the substance to be sensed, and an antibody as thecatching substance can be used. The examples of such combinationsinclude human serum albumin/anti-human serum albumin antibody and humanimmunoglobulin/anti-human immunoglobulin antibody. Whereas, the othersensor portion 13 is used as a reference sensor portion 13R, to thediaphragm of which no catching substance is applied.

[0159] Both sensor portions 13D and 13R are immersed in or placed on thesame specimen. In many cases, since specimens are fluids such as liquidsor gases, the specimens can be tested by comparing the signals from thesensor portions 13D and 13R, without being influenced by the physicalproperties of the specimens such as type and, flow, and temperature ofthe fluid, or the testing environment.

[0160] When this mass sensor 1 is immersed in, for example, a conductiveliquid specimen, if the mass sensor 1 is immersed in the specimen to thelevel where the position sensor electrodes 4, 5 are short-circuited, thediaphragms 19 of the sensor portions 13D and 13R are immersed in thespecimen, but the sensing portion 29 is not short-circuited by thespecimen. However, when the piezoelectric element 25 and the electrodeleads 9, 10 are coated by insulating glass or resin, the areas of themass sensor 1 other than terminals 11, 12, or other connectors, can beimmersed in the specimen.

[0161] Thus, when the substance to be sensed in the specimen reacts withand is caught by the catching substance, the mass of the diaphragm 19 inthe detection sensor portion 13D increases, and the resonant frequencyof the resonating portion 26 varies accompanying this increase in themass of the diaphragm 19. Therefore, on the contrary, by observingchange in the resonant frequency of the resonating portion 26, whetheror not the substance to be sensed has been caught on the diaphragm 19,that is, whether or not the substance to be sensed was present in thespecimen, can be determined, and increase in the mass can be measured.

[0162] In the method for using the two sensor portions 13 as a detectionsensor portion 13D and a reference sensor portion 13R, if the resonatingportion in the reference sensor portion 13R, that is, the diaphragm,connection plate, sensing plate, piezoelectric element, and spring plateare coated by Teflon, the adhesion of the substance to be sensed to thereference sensor portion 13R can be prevented, and more accuratemeasurement can be performed. If the detection sensor portion 13D otherthan the diaphragm 19 is similarly coated by Teflon, the substance to besensed can be caught only on the diaphragm 19, and sensitivity iselevated. Furthermore, it is economically preferable to coat the entiresensor substrate 2 other than the diaphragm 19 with Teflon in order toapply an expensive catching substance such as an antibody only to arequired location.

[0163] When the mass sensor 1 is immersed in a specimen, such as aliquid, or a diaphragm 19 is dipped in a catching substance for applyingthe catching substance to the diaphragm 19, the structure is adopted inwhich two sensor portions 13 are arranged in the lateral direction ofthe sensor substrate 2 horizontal direction) in FIG. 11, so that the twosensor portions 13 are simultaneously immersed in the specimen.

[0164] However, if the two sensor portions 13 are arranged in theperpendicular direction of the sensor substrate 2 (up-down direction),that is, on the position where the detection sensor portion 13D is firstimmersed in the liquid, and the reference sensor portion 13R is notimmersed in the liquid, the process can easily be performed, in whichonly the area of the detection sensor portion 13D is immersed in thecatching substance for applying, and the reference sensor portion 13R isused as a sensor such as a temperature compensating sensor withoutteflon coating, and is not immersed in the catching substance, that isnot to apply the catching substance.

[0165] However, even in using the mass sensor 1 in which the catchingsubstance is applied only to the detection sensor portion 13D, thedetection sensor portion 13D and the reference sensor portion 13R mustbe placed in the same environment on actual mass sensing. Also, when theentire mass sensor 1 is immersed in a conductive liquid, thepiezoelectric elements 25 and the electrode leads 9, 10 in the sensorportions 13R, 13D must obviously be undergone insulation coating.

[0166] The using method, in which the same catching substance is appliedto the diaphragms of both sensor portions 13D and 13R to expand thedynamic range by adding the signals from the sensor portions 13D and13R, is also possible. Furthermore, it is also possible not to use thereference sensor portion 13R for referencing, and a catching substancedifferent from that applied to the detection sensor portion 13D isapplied to the reference sensor portion 13R.

[0167] On the measurement of change in the resonant frequency in themass sensor 1 with these using methods, it is preferable to sense theresonant frequencies in the θ-mode and the φ-mode as described above.For example, as FIG. 14 shows, when the diaphragm 19 generates swingoscillation in the θ-mode about the spring plate 18 and the connectionplate 20 in the plate surface of the diaphragm 19, the movement istransmitted to the sensing plate 21 to cause the bending oscillation ofthe sensing plate 21 and the stretching oscillation of the planerpiezoelectric film 23 in the piezoelectric element 25 on the surface ofthe sensing plate 21, and a constant voltage is generated on the basisof the electrical-mechanical coupling coefficient k₃ (piezoelectricfactor d₃₁ ) of the piezoelectric film 23. When the piezoelectricelement 25 has a comb-shaped electrode structure, a constant voltage isgenerated on the basis of k₃₃(d₃₃). This is the same when the φ-mode isused.

[0168] On the contrary, when an alternating current is applied to thepiezoelectric film 23 through the second electrode 24 and the firstelectrode 22, stretching oscillation is generated in the piezoelectricfilm 23 by d₃₁ or d₃₃ causing the sensing plate 21 to generate bendingoscillation, and the oscillating angle θ of the diaphragm 19 variescorresponding to the mass of the diaphragm 19, and resonant oscillationis generated at a certain frequency. Therefore, the observation ofchange in the resonant frequency is the observation of change in themass of the diaphragm 19, and whether or not a substance to be sensed iscaught on the diaphragm 19 can be determined. By installing twopiezoelectric elements 25 on both plate surfaces of the sensing plate 21and comparing obtained signals, noise can be reduced, the effect ofother oscillation modes can be eliminated, and sensitivity can beimproved.

[0169] Here, in order to further improve the sensitivity of the masssensor 1, change in the resonant frequency of the resonating portion 26must be increased. As a means for this, a method for controlling theratio of masses of the diaphragm 19 and the spring plate 18 can be used.As the spring plate 18 is thinned to reduce the mass, and the mass ratiowith the diaphragm 19 (mass of the diaphragm 19/mass of the spring plate18) is increased, sensitivity is improved.

[0170] However, since the rigidity of the spring plate 18 is loweredwith decrease in the thickness and the mass of the spring plate 18, themass ratio (mass of the diaphragm 19/(mass of the spring plate 18 φmassof the connection plate 20)) is preferably 0.1 or more within a rangewhere the rigidity of the spring plate 18 and the connection plate 20 issecured, considering the thickness and area of the diaphragm 19, but itis preferable to determine the suitable ratio considering the area ofthe diaphragm 19. However, these mass ratios are preferably determinedwithin the range where the conditions of the thickness, width, and theaspect ratio of the spring plate 18 described above are satisfied. Themass sensor 43C shown in FIG. 16(c) is one of the examples.

[0171] As another means for improving sensitivity, a method to decreasethe thickness of the diaphragm 19 for increasing the mass ratio with asubstance to be sensed (mass of the substance to be sensed/mass of thediaphragm 19), that is, the proportion of change in the mass of thediaphragm 19 can be used. Furthermore, when the thickness of thediaphragm 19 is decreased, if the surface area of the diaphragm 19 isincreased without decreasing the mass, the area to which the catchingsubstance is applied can be increased, and more substance to be sensedcan be caught, resulting in the improvement of sensitivity.

[0172] Next, other applications of the mass sensor 1 will be described.First, when the catching substance applied to the diaphragm 19 is amoisture adsorbing material, the mass sensor 1 can be used as a moisturemeter. When applying to the diaphragm 19 an adsorbing material thatadsorbs a specific gaseous component, or an organic or inorganicsubstance as a catching substance, the mass sensor 1 can be used as agas sensor, an odor sensor, or a taste sensor. Furthermore, if thetemperature of the diaphragm 19 is controlled to make moisture condense,the mass sensor I can be used as a dew point meter which measures thedew point from the temperature when the mass of the diaphragm 19 isincreased.

[0173] The mass sensor 1 can also be used as a film thickness meter. Thefilms that can be measured include sputtered films or CVD films formedin vacuum, LB films formed in gases, or electrodeposited films formed inliquids. When these films are formed, if the diaphragm 19 or theresonating portion 26 of the mass sensor 1 is placed in the same filmforming environment, a film is formed on the diaphragm 19 or theresonating portion 26 causing change in the mass, and change in resonantfrequency, the thickness or the growing speed of the formed film can bemeasured.

[0174] Although a quartz vapor deposited film thickness meter has beenknown to detect change in the resonant frequency of a quartz oscillator80 similar to the one shown in FIG. 27 in the slipping direction whenthe film thickness changes, it has problems in that it is affected bychange in temperature, noise due to the collision of impurities, andchange in vacuum pressure, because the oscillator itself is used in avapor deposition environment.

[0175] Whereas, if the mass sensor 1 is used in the θ-mode as a vapordeposited film thickness meter, the sensing portion 29 resists change intemperature because of the rigid body mode, the probability of thecollision of impurities is low because the diaphragm 19 is as thin as 3to 20 Am, and a structure in which the sensing portion 29, spring plate18, and the connection plate 20 are easily held in a constantenvironment, the measurement accuracy can be improved compared with thecase where a quartz oscillator 80 is used.

[0176] Furthermore, the mass sensor 1 can be used as a viscosity meterto cause the shear waves of transverse waves to occur in a fluid whenthe diaphragm 19 is immersed in the liquid, and receive the mass load ofthe portion where viscous waves enter.

[0177] Although a quartz viscosity meter for detecting change in theresonant frequency of a quartz oscillator 80 in the slipping directionis also used, it has problems in that it is affected by change intemperature, and noise due to the collision of impurities in the liquid,because the quartz oscillator 80 itself is immersed in the liquid.

[0178] On the other hand, when the mass sensor 1 is used in the θ-modeas a viscosity meter, since the sensing portion 29, the spring plate 18,and the connection plate 20 are not required to immerse in the liquid,the sensing portion 29 resists change in temperature because of therigid body mode, and the diaphragm 19 is as thin as 3 to 20 μm, theprobability of the collision of impurities is low, sensitivity isimproved.

[0179] Furthermore, a quartz oscillator is used as a friction vacuummeter since its electric resistance varies due to the friction of gasmolecules and the viscous friction of the gas in a vacuum. However,since this type of vacuum meter is used to measure change in frequenciesdue to the mass load effect of the quartz oscillator, the mass sensor 1of the present invention utilizing basically the same measurementprinciple can also be used as a vacuum meter.

[0180] Although a friction vacuum meter using a quartz oscillatordetects change in resistance when the tuning fork-shaped oscillator 90is oscillated in the X-axis direction as FIG. 28 shows, it is difficultto decrease the thickness d₁ of the oscillator 90, and therefore, theimprovement of sensitivity is difficult. Whereas, in the mass sensor 1,the thickness of the diaphragm 19 can be decreased to 3 to 20 μm, andthe θ-mode can be used, sensitivity can be improved.

[0181] In addition, the mass sensor 1 can be used as a temperaturesensor by using the bending mode of the diaphragm 19, that is, bysensing change in the Young's modulus as change in resonant frequency inthe bending mode.

[0182] Although the mass sensor 1 can be used as various sensors, thebasic principle of measurement is to measure change in the resonantfrequency of the resonating portion 26 on the basis of the mass load tothe diaphragm 19. Therefore, a plurality of sensor portions 13 havingdifferent functions can be formed easily in one mass sensor 1. Forexample, the functions of a temperature sensor, a vacuum meter, or aviscosity sensor can be added to the function as the mass sensor 1, thatis, a sensor for referencing for the compensation of temperature,vacuum, or viscosity can be easily incorporated in the mass sensor 1. Insuch cases, since it is not necessary to use a plurality of sensorshaving different shapes for different applications, it is alsoadvantageous from the costs for the incorporation of sensors to theplace of measurement and their handling, and for the measuringinstruments.

[0183] Next, a method for fabricating a mass sensor of the presentinvention will be described using the mass sensor 1 as an example. Asthe materials of the sensor substrate, ceramics such as zirconia aresuitably used. A slurry is produced by mixing a binder, solvent,dispersing agent, and other additives in ceramic powder, and afterremoving foams from the slurry, a green sheet or a green tape for theoscillation plate, intermediate plates and base plates having desiredthickness using a method such as the reverse roll coater method and thedoctor blade method is formed

[0184] Next, these green sheets are punched using a die or laser todesired shapes, for example, as shown in FIG. 23, the shape of anintermediate plate 17 having an opening 14 and a spring plate 18, andthe shape of a base plate 15 having an opening 14, and the green sheetat least one for each of the oscillation plate, the intermediate plate17, and the base plate 15 are laminated in this order, and sintered andintegrated to form the sensor substrate. On laminating these greensheets, holes 8 are formed in each green sheet for the alignment oflamination. The shapes of the green sheets shown in FIG. 23 aresimplified for easy understanding of the formation of the sensor portion13 of the mass sensor 1 shown in FIG. 11.

[0185] Although an opening 14 or a diaphragm 19 can be also formed inthe oscillation plate 3 in green state, since the oscillation plate isas thin as 20 μm or lesser, it is preferable to form the opening 14 orthe diaphragm 19 in a predetermined shape after forming the sensorsubstrate 2 and installing the piezoelectric element 25 by laserprocessing described later, for securing the id; flatness anddimensional accuracy after sintering of the diaphragm 19, connectionplate 20, and sensing plate 21 formed in the oscillation plate 3.

[0186] Methods for installing the piezoelectric element 25 consisting ofa first electrode 22, a piezoelectric film 23, and a second electrode 24on the area of the oscillation plate 3 where the sensing plate 21 isformed include a method in which a piezoelectric film 23 is formed bypress formation using a die or tape formation using a slurry material,the piezoelectric film 23 before sintering is overlaid by heat andpressure on the area of the oscillation plate 3 where the sensing plate21 is formed, and they are simultaneously sintered to form the sensorsubstrate 2 and the piezoelectric film 23 at the same time. In thiscase, however, the electrodes 22, 24 must be formed on the sensorsubstrate 2 or the piezoelectric film 23 beforehand by the filmformation method described later.

[0187] Although the temperature for sintering the piezoelectric film 23is determined depending on the constituting material, it is generally800° C. to 1400° C., preferably 1000° C. to 1400° C. In this case, it ispreferable for controlling the composition of the piezoelectric film 23,that sintering is conducted in the presence of the evaporation source ofthe material for the piezoelectric film 23. When the sintering of thepiezoelectric film 23 and the sintering of the sensor substrate 2 areperformed simultaneously, the sintering conditions of the two must bematched to each other.

[0188] On the other hand, if the film formation method is used, thepiezoelectric element 25 can be installed on the area of the sinteredsensor substrate 2 where the sensing plate 21 is formed, by variousthick film forming methods, such as screen printing, dipping, andpainting; or various thin film forming methods, such as the ion beammethod, sputtering, vacuum deposition, ion plating, chemical vapordeposition (CVD), or electroplating. Among these, for the formation ofthe piezoelectric film 23 in the present invention, thick film formingmethods, such as screen printing, dipping, and painting are preferablyused. This is because the piezoelectric film 23 can be formed usingpaste or slurry consisting mainly of the particles of piezoelectricceramics having an average particle diameter of 0.01 to 5 μm, preferably0.05 to 3 μm, and favorable piezoelectric properties are obtained.

[0189] For example, after the sensor substrate 2 has been sintered underpredetermined conditions, the first electrode 22 is printed and sinteredon the predetermined surface area of the oscillation plate 3, then thepiezoelectric film 23 is printed and sintered, and further, the secondelectrode 24 is printed and sintered to form the piezoelectric element25. Then, electrode leads 9, 10 are printed and sintered for connectingthe electrodes 22, 24 to the measurement apparatus. Here, for example,if platinum (Pt) is used for the first electrode 22, lead zirconatetitanate (PZT) is used for the piezoelectric film 23, gold (Au) is usedfor the second electrode 24, and silver (Ag) is used for the electrodeleads 9, 10, sintering temperatures in the sintering process can belowered stepwise. Therefore, the previously sintered materials are notsintered again in a certain sintering step, and the occurrence oftroubles in the material for electrodes or the like, such as peeling offand aggregation, can be avoided.

[0190] By selecting suitable materials, the respective members of thepiezoelectric element 25 and electrodes 9, 10 can be printed one afterthe other, and integrally sintered at once, or after the piezoelectricfilm 23 is formed, respective electrodes or the like can be formed at alow temperature. Also, the respective members of the piezoelectricelement 25 and electrodes 9, 10 can be formed by a thin film formingmethod, such as sputtering or vapor deposition. In this case, heattreatment is not necessarily required.

[0191] Thus, it is particularly preferable to form the piezoelectricelement 25 using the film formation method, since the piezoelectricelement 25 and the sensing plate 21 can be integrally joined andinstalled without using adhesives, and the mass sensor excels inreliability and reproducibility, and is easily integrated. Here, thepiezoelectric film 23 may be suitably patterned, and the methods forpatterning include, for example, screen printing, photolithography,laser processing, or mechanical processing such as slicing andultrasonic processing.

[0192] Next, a diaphragm 19 is formed on the predetermined area of thusformed sensor substrate. Here, it is preferable to remove theunnecessary part of the oscillation plate 3 by processing using thefourth harmonic of YAG laser. Thus, for example, an opening 14 can beformed leaving members integrally joined to the sensor substrate 2, suchas the diaphragm 19 and the sensing plate 21 as shown in FIG. 11 or 12,and at this time, by adjusting the shape of the diaphragm 19 or thelike, the resonant frequency can be adjusted to the predetermined value,and the range of masses of the substance to be sensed can be determined.

[0193] Here, as shown in FIG. 24 if a part of the diaphragm 19 is cutand removed so that the length of the diaphragm 19 is decreased from L₀to L₁, the resonance point can be raised, and on the other hand, if thewidth of the spring plate 18 and the connection plate 20 is narrowedfrom t₀ to t₁, the resonance point can be lowered. Therefore, by thecombination of these values, the resonance point can be adjusted.Furthermore, by narrowing the width of the diaphragm 19 from W₀ to W₁,the rotation mode can be restricted, the Q value in the θ-mode can beincreased, and the difference of change in the resonant frequenciesdepending on an adhesion location can be decreased even when the mass ofthe adhered substance is the same.

[0194] Furthermore, as FIG. 25 shows, after a piezoelectric element 5comprising a first electrode 22 as the upper electrode, a secondelectrode 24 as the lower electrode, and a piezoelectric film 23 formedtherebetween is once formed, the upper electrode can be removed by thefourth harmonic of YAG laser, or machining to adjust the effectiveelectrode area of the piezoelectric element and adjust sensitivity. Whenthe structure of the piezoelectric element 25 is a comb structure asshown in FIGS. 3 or 4, part of one or both electrodes may be removed.

[0195] In processing such a resonating portion, various processingmethods suitable for the size and shape of the resonating portion, suchas laser processing with YAG laser, the second or third harmonic of YAGlaser, excimer laser, or CO₂ laser; electron beam processing; and dicing(machining), in addition to the fourth harmonic of YAG laser describedabove.

[0196] In addition to the method using green sheets as described above,the sensor substrate 2 can be produced by the compression molding usingmolds, slip casting, or injection molding. In these cases also,machining such as cutting, grinding, laser processing, press punching,and ultrasonic processing is conducted before and after sintering, andthe mass sensor 1 of a predetermined shape is obtained.

[0197] When an insulation coating layer 65 is formed on thepiezoelectric element 25 and electrode leads 9, 10 in thus fabricatedmass sensor 1, as in the mass sensor 43D shown in FIG. 19, it can beformed using glass or a resin by screen printing, painting, or spraying.Here, when glass is used as the material, the mass sensor 1 itself mustbe heated to the softening point of the glass, and since glass has ahigh hardness, oscillation may be inhibited. However, since the resin issoft, and only such processing as drying is required, the use of a resinis preferable. Although it has already been described that fluorine orsilicone resins are suitable as resins that can be used in theinsulation coating layer 65, it is preferable, when these resins areused, to form a primer layer suited to the types of the resin andceramics used, for improving the adhesion with the underlying ceramics,and to form the insulation coating layer 65 on the primer layer.

[0198] Next, when a shield layer 66 formed on the insulation coatinglayer 65 is made of a resin, since sintering is difficult, a method notrequiring heat, such as sputtering, is used when various metallicmaterials are used as conductive members; however, when a conductivepaste comprising metal powder and a resin is used, screen printing orpainting can be used preferably. If the insulation coating layer 65 ismade of glass, a paste containing a metal can be screen-printed, andsintered below a temperature at which the glass flows.

[0199] Finally, a catching substance or the like is applied to theentire diaphragm 19 or resonating portion 26 to complete the mass sensor1. The measurement of resonant frequencies is performed using animpedance analyzer or a network analyzer, or by the SINSWEEP system, orthrough the measurement of transfer functions by oscillating by externalultrasonic waves. Furthermore, change in the mass of the diaphragm 19can be measured from change in the resonant frequencies.

[0200] The present invention will be described below referring to theexample; however, this example is not intended to limit the presentinvention.

[0201] In the fabrication of the mass sensor having the structure shownin FIG. 11, green sheet having different thickness were prepared for theoscillation plate, the intermediate plate, and the base plate fromzirconia which had been partially stabilized by yttrium oxide, processedin predetermined shapes, laminated in this order, heated and compressed,and integrally sintered at 1450° C. Next, a piezoelectric elementconsisting of a first electrode, a piezoelectric film, and a secondelectrode, and electrode leads connected to these electrodes were formedon the predetermined area of the oscillation plate on which the sensingplate was formed by the screen-print method. The first electrode wasmade of platinum; the piezoelectric film was made of a materialcontaining lead zirconate, lead titanate, and lead magnesium niobate asmain components; the second electrode was made of gold; and theelectrode leads were made of silver.

[0202] Next, YAG laser processing (fourth harmonic, wavelength: 266 nm)was performed so that an opening, a diaphragm, and a sensing plate wereformed in the sensor portion 13 shown in FIG. 12 to complete the masssensor 1. Here, the thickness of the diaphragm was 7 μm, the thicknessof the intermediate plate was 65 μm, the thickness of the base plate was150 μm, and the dimension of the diaphragm was 0.5 mm×0.3 mm.

[0203] The mass on the diaphragm was changed by forming a plurality ofspot patterns of 10 μmφ in diameter in a gold layer of a thickness of0.3 μm formed on an entire surface of the diaphragm with YAG laser asdescribed above to decrease the mass. The resonant frequencies beforeand after processing were observed, and the results shown in FIG. 26were obtained. From these results, it was verified that the mass sensorof the present invention exhibited change in resonant frequenciescorresponding to change in the mass of a nanometer order.

[0204] The mass sensor of the present invention has been describedfocussing a piezoelectric conversion device using a piezoelectric filmthat utilizes the piezoelectric effect as a device for sensing theoscillation of a resonating portion and inverting the oscillation toelectric signals. However, such oscillation signal converting devicesare not limited to those utilizing the piezoelectric effect, but may beconstituted by those utilizing electromagnetic induction, change inelectrostatic capacity, change in incident light, change in electricresistance, or pyroelectricity.

[0205] For example, those utilizing electromagnetic induction includethose having a coil installed on the sensing plate, an electric circuitfor detecting electric signals flowing in the coil, and a magnet (may bean electromagnet) for generating a magnetic field in the coil. In thiscase, when the coil oscillates together with the resonating portion, anelectric current flows through the coil due to electromagneticinduction, and the electric current is detected by the electric circuit.Those utilizing change in electrostatic capacity include those having apair of electrodes installed on the surface of the sensing plate, adielectric sandwiched by these electrodes, and an electric circuitconnected to these electrodes, and detecting the electrostatic capacitycharged in this specific space with the electric circuit.

[0206] Those utilizing change in incident light include those having adevice for illuminating the resonating portion such as a photodiode, anda device for measuring the quantity of light reflected by the resonatingportion Light receiver). This light receiver may be a photo sensor. Asthe resonating portion oscillates, the quantity of light reflected bythe resonating portion changes, and change in the quantity of theincident light is measured by the light receiver.

[0207] Those utilizing change in electric resistance are roughly dividedinto that using a conductor and that using a semiconductor. That using aconductor has a conductor provided on the surface of the resonatingportion, and an electric circuit connected to the conductor. Since theconductor is distorted by oscillation when the conductor oscillatestogether with the resonating portion and its resistance changes, thischange in resistance is detected by the electric circuit. That using asemiconductor uses a semiconductor in place of the conductor.

[0208] Those utilizing pyroelectricity include those comprising a pairof electrodes provided on the surface of the sensing plate, apyroelectric member formed between these electrodes, an electroniccircuit connected to the electrodes, and a heat source, and detectingpyroelectric current generated by oscillation with the electroniccircuit.

[0209] These types of oscillation signal converters can be used in placeof the piezoelectric elements described above, and in addition,different signal converters can be used for the excitation of theresonating portion and for receiving the oscillation from the resonatingportion separately. For example, a piezoelectric converter can be usedor exciting, and an electrostatic capacity-type converter for receiving.The arrangement of exciting and receiving devices can be selectedsuitably and conveniently depending on the number of sensing plates. Forexample, when only one sensing plate is used, they can be arranged onthe surface of the sensing plate; when two sensing plates are used, theycan be arranged on both surfaces of the two, or on each surface.

[0210] Industrial Applicability

[0211] As described above, a mass sensor and a method for mass sensingof the present invention, exhibit excellent effects in that change invarious extremely small masses occurring on a diaphragm, that is changein mass load on the diaphragm, can be sensed easily and accurately in ashort time. Therefore, when a catching substance for catching varioussubstances to be sensed is applied to the diaphragm, the mass sensor canbe used as a gas sensor, taste sensor, odor sensor, immune sensor, ormoisture meter, which can sense various chemical substances ormicroorganisms such as bacteria and viruses easily and quickly. Whensuch a catching substance is not applied to the diaphragm, the masssensor can be used as a film thickness meter, viscosity meter, vacuummeter, or thermometer. In addition, when the sensor is used as an immunesensor substituting the dyeing method, an odor sensor, or a tastesensor, the reliability of tests can be improved, because determinationdoes not rely on human sense.

[0212] Also, since the mass sensor of the present invention is littleaffected by the temperature of the specimen or change in the propertiesof materials for the mass sensor itself due to the temperature of thespecimen on sensing resonant frequencies, and can measure an extremelysmall quantity of a 0.1 nanogram order as the nature of its structure,it exhibits the effect for sensing an extremely small quantity ofsubstance.

[0213] Furthermore, although the mass sensor of the present inventioncan be used for various applications as described above, sincemeasurement is performed on the basis of fundamental measurementprinciple in which change in resonant frequencies of the resonatingportion including the diaphragm subjected to mass load are measured, aplurality of resonating portions having different functions can beprovided in a mass sensor easily. Therefore, since the use of aplurality of various discrete sensors is not required, the mass sensorof the present invention also excels in economic effects in thereduction of costs for incorporating the sensor in the measuringlocation, for facilities for handling or measuring such as measuringinstruments, as well as the reduction of costs by the integration andthe shared use of manufacturing equipment.

1. A mass sensor characterized in that a piezoelectric element isarranged on at least a part of at least one plate surface of a sensingplate, a side of at least one sheet-like diaphragm is joined to a sideof said sensing plate so that the plate surface of said diaphragm isperpendicular to the plate surface of said sensing plate, the other sideof said sensing plate is joined to a sensor substrate, and a resonanceportion is formed of said sensing plate, said diaphragm, and saidpiezoelectric element.
 2. A mass sensor characterized in that aconnection plate is joined to a diaphragm at respective sides, twosensing plates are joined to said connection plate at respective sidesin the direction perpendicular to the joining direction of saiddiaphragm and said connection plate so as to sandwich said connectionplate, a piezoelectric element is arranged on at least a part of atleast one of the plate surfaces of at least one of said sensing plates,at least a part of sides of said connection plate and said sensingplates is joined to a side of the sensor substrate, and a resonanceportion is formed of said diaphragm, said connection plate, said sensingplates, and said piezoelectric element.
 3. The mass sensor according toclaim 2 characterized in that said piezoelectric element is arranged onat least one of the plate surfaces of one sensing plate, and one or moreslits are formed on the other sensing plate in the directionperpendicular to the joining direction of said other sensing plate andsaid connection plate.
 4. The mass sensor according to claim 2characterized in that respective piezoelectric elements are arranged onthe plate surfaces of said respective sensing plates in at least thesame direction, and that the polarizing direction of the piezoelectricfilm in said piezoelectric elements arranged on one of the sensingplates, and the polarizing direction of the piezoelectric film in saidpiezoelectric elements arranged on the other sensing plates are oppositeto each other.
 5. A mass sensor characterized in that a connection plateand a sensing plate not directly joined to each other are joined to saiddiaphragm at respective sides so that the joining directions with thediaphragm are parallel to each other, said connection plate and saidsensing plate are joined to one side of a sensor substrate, apiezoelectric element is arranged on at least a part of at least one ofthe plate surfaces of said sensing plate, and a resonance portion isformed of said diaphragm, said connection plate, said sensing plate, andsaid piezoelectric element.
 6. A mass sensor characterized in that anassembly of a diaphragm sandwiched with two connection plates by joiningat respective sides is placed across the side surfaces of a depressionformed on a sensor substrate, each of two sensing plates is placedacross said connection plate and across the bottom side of saiddepression in the direction perpendicular to the direction of saidrespective connection plates sandwiching said diaphragm, a piezoelectricelement is arranged on at least a part of at least one of the platesurfaces of said sensing plates, and a resonance portion is formed ofsaid diaphragm, said connection plate, said sensing plates, and saidpiezoelectric element.
 7. A mass sensor characterized in that anassembly of a diaphragm sandwiched with two connection plates by joiningat respective sides is placed across a through-hole formed on a sensorsubstrate, at least a plurality of sensing plates are placed betweensaid respective connection plates and the side of said through-hole, orsaid diaphragm and the side of said through-hole, in the directionperpendicular to the direction of said respective connection platessandwiching said diaphragm, a piezoelectric element is arranged on atleast a part of at least one of the plate surfaces of at least one ofsaid sensing plates, and a resonance portion is formed of saiddiaphragm, said connection plates, said sensing plates, and saidpiezoelectric element.
 8. The mass sensor according to claim 7characterized in that, in each pair of said respective sensing platesfacing to each other via said respective connection plates or saiddiaphragm, said piezoelectric element is arranged on at least one of theplate surfaces of one sensing plate, and one or more slits are formed onthe other sensing plate in the direction perpendicular to the joiningdirection of said other sensing plate and said connection plates or saiddiaphragm.
 9. The mass sensor according to claim 7 characterized in thatrespective piezoelectric elements are arranged on the plate surface ofeach pair of said respective sensing plates facing to each other viasaid respective connection plates or said diaphragm in at least the samedirection, and that the polarizing direction of the piezoelectric filmin said piezoelectric elements arranged on one of the sensing plates,and the polarizing direction of the piezoelectric film in saidpiezoelectric elements arranged on the other sensing plate is oppositeto each other.
 10. The mass sensor according to claim 2 characterized inthat said diaphragm, said connection plate, and said sensing plate forma same plane through joining to each other.
 11. The mass sensoraccording to claim 5 characterized in that said diaphragm, saidconnection plate, and said sensing plate form a same plane throughjoining to each other.
 12. The mass sensor according to claim 6characterized in that said diaphragm, said connection plate, and saidsensing plate form a same plane through joining to each other.
 13. Themass sensor according to claim 7 characterized in that said diaphragm,said connection plate, and said sensing plate form a same plane throughjoining to each other.
 14. The mass sensor according to claim 2characterized in that said sensing plate is fitted in and joined to thedepression formed by said connection plate and said sensor substrate.15. The mass sensor according to claim 5 characterized in that saidsensing plate is fitted in and joined to the depression formed by saidconnection plate and said sensor substrate.
 16. The mass sensoraccording to claim 6 characterized in that said sensing plate is fittedin and joined to the depression formed by said connection plate and saidsensor substrate.
 17. The mass sensor according to claim 7 characterizedin that said sensing plate is fitted in and joined to the depressionformed by said connection plate and said sensor substrate.
 18. The masssensor according to claim 2 characterized in that said diaphragm, saidconnection plate, and said sensing plate are integrally formed from anoscillation plate, and said sensor substrate is laminated integrallywith said oscillation plate and base plate.
 19. The mass sensoraccording to claim 5 characterized in that said diaphragm, saidconnection plate, and said sensing plate are integrally formed from anoscillation plate, and said sensor substrate is laminated integrallywith said oscillation plate and base plate.
 20. The mass sensoraccording to claim 6 characterized in that said diaphragm, saidconnection plate, and said sensing plate are integrally formed from anoscillation plate, and said sensor substrate is laminated integrallywith said oscillation plate and base plate.
 21. The mass sensoraccording to claim 7 characterized in that said diaphragm, saidconnection plate, and said sensing plate are integrally formed from anoscillation plate, and said sensor substrate is laminated integrallywith said oscillation plate and base plate.
 22. The mass sensoraccording to claim 2 characterized in that a spring plate is bonded toone of or each of plate surfaces of said connection plate, and saidspring plate is joined to said sensor substrate or the spring platereinforcement.
 23. The mass sensor according to claim 5 characterized inthat a spring plate is bonded to one of or each of plate surfaces ofsaid connection plate, and said spring plate is joined to said sensorsubstrate or the spring plate reinforcement.
 24. The mass sensoraccording to claim 6 characterized in that a spring plate is bonded toone of or each of plate surfaces of said connection plate, and saidspring plate is joined to said sensor substrate or the spring platereinforcement.
 25. The mass sensor according to claim 7 characterized inthat a spring plate is bonded to one of or each of plate surfaces ofsaid connection plate, and said spring plate is joined to said sensorsubstrate or the spring plate reinforcement.
 26. The mass sensoraccording to claim 22 characterized in that said spring plate isintegrally formed with said respective connection plate while beingintegrally formed with an intermediate plate integrally inserted betweensaid oscillation plate and said base plate, or being integrally formedwith the spring plate reinforcement integrally formed with saidoscillation plate.
 27. The mass sensor according to claim 23characterized in that said spring plate is integrally formed with saidrespective connection plate while being integrally formed with anintermediate plate integrally inserted between said oscillation plateand said base plate, or being integrally formed with the spring platereinforcement integrally formed with said oscillation plate.
 28. Themass sensor according to claim 24 characterized in that said springplate is integrally formed with said respective connection plate whilebeing integrally formed with an intermediate plate integrally insertedbetween said oscillation plate and said base plate, or being integrallyformed with the spring plate reinforcement integrally formed with saidoscillation plate.
 29. The mass sensor according to claim 25characterized in that said spring plate is integrally formed with saidrespective connection plate while being integrally formed with anintermediate plate integrally inserted between said oscillation plateand said base plate, or being integrally formed with the spring platereinforcement integrally formed with said oscillation plate.
 30. Themass sensor according to claim 22 characterized in that said mass sensoris bonded to said spring plate, and has a reinforcing plate joined tothe side of said sensor substrate.
 31. The mass sensor according toclaim 23 characterized in that said mass sensor is bonded to said springplate, and has a reinforcing plate joined to the side of said sensorsubstrate.
 32. The mass sensor according to claim 24 characterized inthat said mass sensor is bonded to said spring plate, and has areinforcing plate joined to the side of said sensor substrate.
 33. Themass sensor according to claim 25 characterized in that said mass sensoris bonded to said spring plate, and has a reinforcing plate joined tothe side of said sensor substrate.
 34. The mass sensor according toclaim 30 characterized in that said reinforcing plate is integrallyformed with said spring plate and said sensor substrate.
 35. The masssensor according to claim 31 characterized in that said reinforcingplate is integrally formed with said spring plate and said sensorsubstrate.
 36. The mass sensor according to claim 32 characterized inthat said reinforcing plate is integrally formed with said spring plateand said sensor substrate.
 37. The mass sensor according to claim 33characterized in that said reinforcing plate is integrally formed withsaid spring plate and said sensor substrate.
 38. The mass sensoraccording to claim 1 characterized in that a catching substance reactingonly with a substance to be sensed and catching said substance to besensed is applied on at least a part of said diaphragm, saidpiezoelectric element measures the resonant frequency of said resonatingportion in the state when said substance to be sensed has not beencaught by said catching substance, and in the state after said substanceto be sensed has been caught by said catching substance, and the mass ofsaid substance to be sensed caught by said catching substance ismeasured from change in the measured resonant frequency.
 39. The masssensor according to claim 2 characterized in that a catching substancereacting only with a substance to be sensed and catching said substanceto be sensed is applied on at least a part of said diaphragm, saidpiezoelectric element measures the resonant frequency of said resonatingportion in the state when said substance to be sensed has not beencaught by said catching substance, and in the state after said substanceto be sensed has been caught by said catching substance, and the mass ofsaid substance to be sensed caught by said catching substance ismeasured from change in the measured resonant frequency.
 40. The masssensor according to claim 5 characterized in that a catching substancereacting only with a substance to be sensed and catching said substanceto be sensed is applied on at least a part of said diaphragm, saidpiezoelectric element measures the resonant frequency of said resonatingportion in the state when said substance to be sensed has not beencaught by said catching substance, and in the state after said substanceto be sensed has been caught by said catching substance, and the mass ofsaid substance to be sensed caught by said catching substance ismeasured from change in the measured resonant frequency.
 41. The masssensor according to claim 6 characterized in that a catching substancereacting only with a substance to be sensed and catching said substanceto be sensed is applied on at least a part of said diaphragm, saidpiezoelectric element measures the resonant frequency of said resonatingportion in the state when said substance to be sensed has not beencaught by said catching substance, and in the state after said substanceto be sensed has been caught by said catching substance, and the mass ofsaid substance to be sensed caught by said catching substance ismeasured from change in the measured resonant frequency.
 42. The masssensor according to claim 7 characterized in that a catching substancereacting only with a substance to be sensed and catching said substanceto be sensed is applied on at least a part of said diaphragm, saidpiezoelectric element measures the resonant frequency of said resonatingportion in the state when said substance to be sensed has not beencaught by said catching substance, and in the state after said substanceto be sensed has been caught by said catching substance, and the mass ofsaid substance to be sensed caught by said catching substance ismeasured from change in the measured resonant frequency.
 43. The masssensor according to claim 38 characterized in that at least tworesonating portions are placed on said sensor substrate, and saidcatching substance is not applied to the diaphragm of at least one ofsaid resonating portions.
 44. The mass sensor according to claim 39characterized in that at least two resonating portions are placed onsaid sensor substrate, and said catching substance is not applied to thediaphragm of at least one of said resonating portions.
 45. The masssensor according to claim 40 characterized in that at least tworesonating portions are placed on said sensor substrate, and saidcatching substance is not applied to the diaphragm of at least one ofsaid resonating portions.
 46. The mass sensor according to claim 41characterized in that at least two resonating portions are placed onsaid sensor substrate, and said catching substance is not applied to thediaphragm of at least one of said resonating portions.
 47. The masssensor according to claim 42 characterized in that at least tworesonating portions are placed on said sensor substrate, and saidcatching substance is not applied to the diaphragm of at least one ofsaid resonating portions.
 48. The mass sensor according to claim 38characterized in that at least two resonating portions are placed onsaid sensor substrate, and each of different catching substances isapplied to at least a part of each of the diaphragms of said resonatingportions.
 49. The mass sensor according to claim 39 characterized inthat at least two resonating portions are placed on said sensorsubstrate, and each of different catching substances is applied to atleast a part of each of the diaphragms of said resonating portions. 50.The mass sensor according to claim 40 characterized in that at least tworesonating portions are placed on said sensor substrate, and each ofdifferent catching substances is applied to at least a part of each ofthe diaphragms of said resonating portions.
 51. The mass sensoraccording to claim 41 characterized in that at least two resonatingportions are placed on said sensor substrate, and each of differentcatching substances is applied to at least a part of each of thediaphragms of said resonating portions.
 52. The mass sensor according toclaim 42 characterized in that at least two resonating portions areplaced on said sensor substrate, and each of different catchingsubstances is applied to at least a part of each of the diaphragms ofsaid resonating portions.
 53. The mass sensor according to claim 1characterized in that at least two resonating portions are placed onsaid sensor substrate, and the dynamic range is expanded by integratingthe signals from said respective resonating portions.
 54. The masssensor according to claim 2 characterized in that at least tworesonating portions are placed on said sensor substrate, and the dynamicrange is expanded by integrating the signals from said respectiveresonating portions.
 55. The mass sensor according to claim 5characterized in that at least two resonating portions are placed onsaid sensor substrate, and the dynamic range is expanded by integratingthe signals from said respective resonating portions.
 56. The masssensor according to claim 6 characterized in that at least tworesonating portions are placed on said sensor substrate, and the dynamicrange is expanded by integrating the signals from said respectiveresonating portions.
 57. The mass sensor according to claim 7characterized in that at least two resonating portions are placed onsaid sensor substrate, and the dynamic range is expanded by integratingthe signals from said respective resonating portions.
 58. The masssensor according to claim 1 characterized in that a through-hole of anoptional shape is formed inside said sensor substrate, and saidresonating portion is formed on the internal circumferential surface ofsaid through-hole.
 59. The mass sensor according to claim 2characterized in that a through-hole of an optional shape is formedinside said sensor substrate, and said resonating portion is formed onthe internal circumferential surface of said through-hole.
 60. The masssensor according to claim 5 characterized in that a through-hole of anoptional shape is formed inside said sensor substrate, and saidresonating portion is formed on the internal circumferential surface ofsaid through-hole.
 61. The mass sensor according to claim 6characterized in that a through-hole of an optional shape is formedinside said sensor substrate, and said resonating portion is formed onthe internal circumferential surface of said through-hole.
 62. The masssensor according to claim 7 characterized in that a through-hole of anoptional shape is formed inside said sensor substrate, and saidresonating portion is formed on the internal circumferential surface ofsaid through-hole.
 63. The mass sensor according to claim 1characterized in that one of said piezoelectric element is split intotwo portions, one being used for driving and the other being used forsensing.
 64. The mass sensor according to claim 2 characterized in thatone of said piezoelectric element is split into two portions, one beingused for driving and the other being used for sensing.
 65. The masssensor according to claim 5 characterized in that one of saidpiezoelectric element is split into two portions, one being used fordriving and the other being used for sensing.
 66. The mass sensoraccording to claim 6 characterized in that one of said piezoelectricelement is split into two portions, one being used for driving and theother being used for sensing.
 67. The mass sensor according to claim 7characterized in that one of said piezoelectric element is split intotwo portions, one being used for driving and the other being used forsensing.
 68. The mass sensor according to claim 1 characterized in thattwo piezoelectric elements are placed on one resonating portion, one ofthe piezoelectric elements being used for driving and the other beingused for sensing.
 69. The mass sensor according to claim 2 characterizedin that two piezoelectric elements are placed on one resonating portion,one of the piezoelectric elements being used for driving and the otherbeing used for sensing.
 70. The mass sensor according to claim 5characterized in that two piezoelectric elements are placed on oneresonating portion, one of the piezoelectric elements being used fordriving and the other being used for sensing.
 71. The mass sensoraccording to claim 6 characterized in that two piezoelectric elementsare placed on one resonating portion, one of the piezoelectric elementsbeing used for driving and the other being used for sensing.
 72. Themass sensor according to claim 7 characterized in that two piezoelectricelements are placed on one resonating portion, one of the piezoelectricelements being used for driving and the other being used for sensing.73. The mass sensor according to claim 1 characterized in that aposition sensor consisting of a pair of electrodes is provided on themiddle between said diaphragm and said piezoelectric element on thesensor substrate.
 74. The mass sensor according to claim 2 characterizedin that a position sensor consisting of a pair of electrodes is providedon the middle between said diaphragm and said piezoelectric element onthe sensor substrate.
 75. The mass sensor according to claim 5characterized in that a position sensor consisting of a pair ofelectrodes is provided on the middle between said diaphragm and saidpiezoelectric element on the sensor substrate.
 76. The mass sensoraccording to claim 6 characterized in that a position sensor consistingof a pair of electrodes is provided on the middle between said diaphragmand said piezoelectric element on the sensor substrate.
 77. The masssensor according to claim 7 characterized in that a position sensorconsisting of a pair of electrodes is provided on the middle betweensaid diaphragm and said piezoelectric element on the sensor substrate.78. The mass sensor according to claim 1 characterized in that electrodeleads connecting to said piezoelectric element, the electrode of saidpiezoelectric element are coated with a resin or glass insulationcoating layer.
 79. The mass sensor according to claim 2 characterized inthat electrode leads connecting to said piezoelectric element, theelectrode of said piezoelectric element are coated with a resin or glassinsulation coating layer.
 80. The mass sensor according to claim 5characterized in that electrode leads connecting to said piezoelectricelement, the electrode of said piezoelectric element are coated with aresin or glass insulation coating layer.
 81. The mass sensor accordingto claim 6 characterized in that electrode leads connecting to saidpiezoelectric element, the electrode of said piezoelectric element arecoated with a resin or glass insulation coating layer.
 82. The masssensor according to claim 7 characterized in that electrode leadsconnecting to said piezoelectric element, the electrode of saidpiezoelectric element are coated with a resin or glass insulationcoating layer.
 83. The mass sensor according to claim 78 characterizedin that said resin is a fluorine resin or a silicone resin.
 84. The masssensor according to claim 79 characterized in that said resin is afluorine resin or a silicone resin.
 85. The mass sensor according toclaim 80 characterized in that said resin is a fluorine resin or asilicone resin.
 86. The mass sensor according to claim 81 characterizedin that said resin is a fluorine resin or a silicone resin.
 87. The masssensor according to claim 82 characterized in that said resin is afluorine resin or a silicone resin.
 88. The mass sensor according toclaim 78 characterized in that a shield layer consisting of a conductivematerial is further formed on the surface of said insulation coatinglayer.
 89. The mass sensor according to claim 79 characterized in that ashield layer consisting of a conductive material is further formed onthe surface of said insulation coating layer.
 90. The mass sensoraccording to claim 80 characterized in that a shield layer consisting ofa conductive material is further formed on the surface of saidinsulation coating layer.
 91. The mass sensor according to claim 81characterized in that a shield layer consisting of a conductive materialis further formed on the surface of said insulation coating layer. 92.The mass sensor according to claim 82 characterized in that a shieldlayer consisting of a conductive material is further formed on thesurface of said insulation coating layer.
 93. The mass sensor accordingto claim 1 characterized in that said sensor substrate, said diaphragm,said connection plate, said sensing plate, and said spring plate arecomposed of stabilized zirconia or partially stabilized zirconia. 94.The mass sensor according to claim 2 characterized in that said sensorsubstrate, said diaphragm, said connection plate, said sensing plate,and said spring plate are composed of stabilized zirconia or partiallystabilized zirconia.
 95. The mass sensor according to claim 5characterized in that said sensor substrate, said diaphragm, saidconnection plate, said sensing plate, and said spring plate are composedof stabilized zirconia or partially stabilized zirconia.
 96. The masssensor according to claim 6 characterized in that said sensor substrate,said diaphragm, said connection plate, said sensing plate, and saidspring plate are composed of stabilized zirconia or partially stabilizedzircorna.
 97. The mass sensor according to claim 7 characterized in thatsaid sensor substrate, said diaphragm, said connection plate, saidsensing plate, and said spring plate are composed of stabilized zirconiaor partially stabilized zirconia.
 98. The mass sensor according to claim1 characterized in that the piezoelectric film in said piezoelectricelement is composed of a material containing a component mainlyconsisting of lead zirconate, lead titanate, and lead magnesium niobate.99. The mass sensor according to claim 2 characterized in that thepiezoelectric film in said piezoelectric element is composed of amaterial containing a component mainly consisting of lead zirconate,lead titanate, and lead magnesium niobate.
 100. The mass sensoraccording to claim 5 characterized in that the piezoelectric film insaid piezoelectric element is composed of a material containing acomponent mainly consisting of lead zirconate, lead titanate, and leadmagnesium niobate.
 101. The mass sensor according to claim 6characterized in that the piezoelectric film in said piezoelectricelement is composed of a material containing a component mainlyconsisting of lead zirconate, lead titanate, and lead magnesium niobate.102. The mass sensor according to claim 7 characterized in that thepiezoelectric film in said piezo electric element is composed of amaterial containing a component mainly consisting of lead zirconate,lead titanate, and lead magnesium niobate.
 103. The mass sensoraccording to claim 1 characterized in that the shapes of at least someof said diaphragm, said connection plate, said sensing plate, or saidspring plate are dimensionally adjusted by trimming with laserprocessing or machining.
 104. The mass sensor according to claim 2characterized in that the shapes of at least some of said diaphragm,said connection plate, said sensing plate, or said spring plate aredimensionally adjusted by trimming with laser processing or machining.105. The mass sensor according to claim 5 characterized in that theshapes of at least some of said diaphragm, said connection plate, saidsensing plate, or said spring plate are dimensionally adjusted bytrimming with laser processing or machining.
 106. The mass sensoraccording to claim 6 characterized in that the shapes of at least someof said diaphragm, said connection plate, said sensing plate, or saidspring plate are dimensionally adjusted by trimming with laserprocessing or machining.
 107. The mass sensor according to claim 7characterized in that the shapes of at least some of said diaphragm,said connection plate, said sensing plate, or said spring plate aredimensionally adjusted by trimming with laser processing or machining.108. The mass sensor according to claim 1 characterized in that theelectrode of said piezoelectric element is laser-processed or machinedto adjust the effective electrode area of said piezoelectric element.109. The mass sensor according to claim 2 characterized in that theelectrode of said piezoelectric element is laser-processed or machinedto adjust the effective electrode area of said piezoelectric element.110. The mass sensor according to claim 5 characterized in that theelectrode of said piezoelectric element is laser-processed or machinedto adjust the effective electrode area of said piezoelectric element.111. The mass sensor according to claim 6 characterized in that theelectrode of said piezoelectric element is laser-processed or machinedto adjust the effective electrode area of said piezoelectric element.112. The mass sensor according to claim 7 characterized in that theelectrode of said piezoelectric element is laser-processed or machinedto adjust the effective electrode area of said piezoelectric element.113. A method for sensing the mass with the mass sensor in which a sideof at least one sheet-like diaphragm is joined to a side of said sensingplate so that the plate surface of said diaphragm is perpendicular tothe plate surface of said sensing plate on which a piezoelectric elementis installed, and the other side of said sensing plate is joined to thesensor substrate, characterized in measuring with said piezoelectricelement resonant frequency on the basis of at least either one of, theθ-mode swing oscillation of said diaphragm in which said diaphragm makespendulum-like oscillation centered on the perpendicular axisperpendicularly passing through the center of a fixed plane, which isthe joining surface of said diaphragm and said sensing plate, in thedirection perpendicular to the side of said diaphragm and alsoperpendicular to said perpendicular axis, the φ-mode swing oscillationof said diaphragm in which said diaphragm makes pendulum-likeoscillation centered on said perpendicular axis with the swing in thedirection perpendicular to the side of said diaphragm and alsoperpendicular to said perpendicular axis accompanied by the swing in thedirection parallel to the side of said diaphragm, or the oscillation ofsaid diaphragm in the direction of said perpendicular axis.
 114. Amethod for sensing the mass with the mass sensor having at least onepiezoelectric element, in which a connection plate is joined to adiaphragm at respective sides, at least one sensing plate is joined tosaid connection plate at respective sides in the direction perpendicularto the joining direction of said diaphragm and said connection plate,and at least a part of sides of said connection plate and said sensingplate is joined to a side of the sensor substrate, characterized inmeasuring with said piezoelectric element resonant frequency on thebasis of at least either one of, the θ-mode swing oscillation of saiddiaphragm in which said diaphragm makes pendulum-like oscillationcentered on the perpendicular axis perpendicularly passing through thecenter of a fixed plane, which is the joining surface of said connectionplate and said sensor substrate, in the direction perpendicular to theside of said diaphragm and also perpendicular to said perpendicularaxis, or the φ-mode swing oscillation of said diaphragm in which saiddiaphragm makes pendulum-like oscillation centered on said perpendicularaxis with the swing in the direction perpendicular to the side of saiddiaphragm and also perpendicular to said perpendicular axis accompaniedby the swing in the direction parallel to the side of said diaphragm.115. A method for sensing the mass with the mass sensor having at leastone piezoelectric element, in which an assembly of a diaphragmsandwiched with two connection plates by joining at respective sides isplaced across the side surfaces of a depression or across a through-holeformed on a sensor substrate, at least a plurality of sensing plates areplaced between said respective connection plates and the bottom side ofsaid depression or the side of said through-hole, or between saiddiaphragm and the bottom side of said depression or the side of saidthrough-hole, in the direction perpendicular to the direction of saidrespective connection plates sandwiching said diaphragm, characterizedin measuring with said piezoelectric element resonant frequency on thebasis of at least either one of the θ-mode swing oscillation of saiddiaphragm in which said diaphragm makes pendulum-like oscillationcentered on the perpendicular axis perpendicularly passing through thecenter of a fixed plane, which is the joining surface of said connectionplate and said sensor substrate, in the direction perpendicular to theside of said diaphragm and also perpendicular to said perpendicularaxis, the φ-mode swing oscillation of said diaphragm in which saiddiaphragm makes pendulum-like oscillation centered on said perpendicularaxis with the swing in the direction perpendicular to the side of saiddiaphragm and also perpendicular to said perpendicular axis accompaniedby the swing in the direction parallel to the side of said diaphragm,the swing oscillation of said diaphragm centered on said perpendicularaxis, oscillating parallel to the direction perpendicular to the side ofsaid diaphragm and also perpendicular to said perpendicular axis, or therotating oscillation of said diaphragm in the plate surface of saiddiaphragm.